Primary bedaquiline resistance in Karakalpakstan, Uzbekistan

BACKGROUND: Bedaquiline (BDQ) is widely used in the treatment of rifampicin-resistant TB (RR-TB). However, resistance to BDQ is now emerging. There are no standardised regimens for BDQ-resistant TB. This study aims to share experience in managing primary BDQ-resistant TB.METHODS: We performed a retrospective study of patients treated for RR-TB in Karakalpakstan, Uzbekistan, from January 2017 to March 2022. We identified patients with resistance to BDQ with no history of BDQ exposure. We describe baseline characteristics, treatment and follow-up of these patients.RESULTS: Twelve of the 1,930 patients (0.6%) had baseline samples resistant to BDQ with no history of BDQ exposure, 75% (9/12) of whom had been previously treated for TB. Ten (83.3%) were resistant to fluoroquinolones; respectively 66% and 50% had culture conversion by Month 3 and Month 6. The interim treatment outcomes were as follows: unfavourable treatment outcomes (3/12, 25%), favourable outcomes (2/12, 17%); the remaining seven (58%) were continuing treatment.CONCLUSIONS: A large proportion of the cases had previously been treated for TB and had TB resistant to quinolone. Both patients who had not experienced culture conversion by Month 3 had an unfavourable treatment outcome. Therefore, we recommend monthly monitoring of culture status for patients on treatment regimens for BDQ resistance.

Top 2020 studies relevant to primary care: From the PEER team

OBJECTIVE

To summarize high-quality studies for 10 topics from 2020 that have strong relevance to primary care practice.

SELECTING THE EVIDENCE

Study selection involved routine literature surveillance by a group of primary health care professionals. This included screening abstracts of high-impact journals and EvidenceAlerts, as well as searching the American College of Physicians Journal Club.

MAIN MESSAGE

Topics of the 2020 articles most likely to affect primary care practice included whether antibiotic prophylaxis reduces maternal infections following operative vaginal birth; which second-line agent after metformin reduces cardiovascular outcomes for patients with diabetes; whether gabapentin is effective for alcohol use disorder; whether compression stockings prevent recurrent cellulitis; guideline recommendations for management of dyslipidemia to reduce cardiovascular risk; whether intermittent fasting is superior to consistent mealtimes for weight loss; whether vitamin C added to iron supplementation increases hemoglobin more than iron alone; whether antacid-lidocaine combinations are superior to antacid alone for epigastric pain; whether dapagliflozin improves renal and cardiovascular outcomes in chronic kidney disease; and whether empagliflozin improves cardiovascular outcomes in patients with heart failure. Five "runner-up" studies are also briefly reviewed.

CONCLUSION

Research from 2020 produced several high-quality studies in diabetes and cardiovascular disease, but also included a variety of other conditions relevant to primary care such as vaginal operative births, alcohol use disorder, weight loss, and chronic leg edema.

PEER systematic review of randomized controlled trials: Management of chronic neuropathic pain in primary care

OBJECTIVE

To determine the proportion of patients with neuropathic pain who achieve a clinically meaningful improvement in their pain with the use of different pharmacologic and nonpharmacologic treatments.

DATA SOURCES

MEDLINE, EMBASE, the Cochrane Library, and a gray literature search.

STUDY SELECTION

Randomized controlled trials that reported a responder analysis of adults with neuropathic pain-specifically diabetic neuropathy, postherpetic neuralgia, or trigeminal neuralgia-treated with any of the following 8 treatments: exercise, acupuncture, serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), topical rubefacients, opioids, anticonvulsant medications, and topical lidocaine.

SYNTHESIS

A total of 67 randomized controlled trials were included. There was moderate certainty of evidence that anticonvulsant medications (risk ratio of 1.54; 95% CI 1.45 to 1.63; number needed to treat [NNT] of 7) and SNRIs (risk ratio of 1.45; 95% CI 1.33 to 1.59; NNT = 7) might provide a clinically meaningful benefit to patients with neuropathic pain. There was low certainty of evidence for a clinically meaningful benefit for rubefacients (ie, capsaicin; NNT = 7) and opioids (NNT = 8), and very low certainty of evidence for TCAs. Very low-quality evidence demonstrated that acupuncture was ineffective. All drug classes, except TCAs, had a greater likelihood of deriving a clinically meaningful benefit than having withdrawals due to adverse events (number needed to harm between 12 and 15). No trials met the inclusion criteria for exercise or lidocaine, nor were any trials identified for trigeminal neuralgia.

CONCLUSION

There is moderate certainty of evidence that anticonvulsant medications and SNRIs provide a clinically meaningful reduction in pain in those with neuropathic pain, with lower certainty of evidence for rubefacients and opioids, and very low certainty of evidence for TCAs. Owing to low-quality evidence for many interventions, future high-quality trials that report responder analyses will be important to strengthen understanding of the relative benefits and harms of treatments in patients with neuropathic pain.

PEER systematic review of randomized controlled trials: Management of chronic low back pain in primary care

OBJECTIVE

To determine the proportion of chronic low back pain patients who achieve a clinically meaningful response from different pharmacologic and nonpharmacologic treatments.

DATA SOURCES

MEDLINE, EMBASE, Cochrane Library, and gray literature search.

STUDY SELECTION

Published randomized controlled trials (RCTs) that reported a responder analysis of adults with chronic low back pain treated with any of the following 15 interventions: oral or topical nonsteroidal anti-inflammatory drugs (NSAIDs), exercise, acupuncture, spinal manipulation therapy, corticosteroid injections, acetaminophen, oral opioids, anticonvulsants, tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors (SNRIs), selective serotonin reuptake inhibitors, cannabinoids, oral muscle relaxants, or topical rubefacients.

SYNTHESIS

A total of 63 RCTs were included. There was moderate certainty that exercise (risk ratio [RR] of 1.71; 95% CI 1.37 to 2.15; number needed to treat [NNT] of 7), oral NSAIDs (RR = 1.44; 95% CI 1.17 to 1.78; NNT = 6), and SNRIs (duloxetine; RR = 1.25; 95% CI 1.13 to 1.38; NNT = 10) provide clinically meaningful benefits to patients with chronic low back pain. Exercise was the only intervention with sustained benefit (up to 48 weeks). There was low certainty that spinal manipulation therapy and topical rubefacients benefit patients. The benefit of acupuncture disappeared in higher-quality, longer (> 4 weeks) trials. Very low-quality evidence demonstrated that corticosteroid injections are ineffective. Patients treated with opioids had a greater likelihood of discontinuing treatment owing to an adverse event (number needed to harm of 5) than continuing treatment to derive any clinically meaningful benefit (NNT = 16), while those treated with SNRIs (duloxetine) had a similar likelihood of continuing treatment to attain benefit (NNT = 10) as those discontinuing the medication owing to an adverse event (number need to harm of 11). One trial each of anticonvulsants and topical NSAIDs found similar benefit to that of placebo. No RCTs of acetaminophen, cannabinoids, muscle relaxants, selective serotonin reuptake inhibitors, or tricyclic antidepressants met the inclusion criteria.

CONCLUSION

Exercise, oral NSAIDs, and SNRIs (duloxetine) provide a clinically meaningful reduction in pain, with exercise being the only intervention that demonstrated sustained benefit after the intervention ended. Future high-quality trials that report responder analyses are required to provide a better understanding of the benefits and harms of interventions for patients with chronic low back pain.

Using a behavioural framework to optimize antibiotic prescribing by family medicine residents

This article was migrated. The article was marked as recommended. Background and objectives:Overprescribing of antibiotics in primary care is a prominent concern in the context of increasing antimicrobial resistance worldwide. Medical trainees are a key group to deliver thoughtful antimicrobial stewardship training. This study examined the factors influencing antibiotic prescribing for upper respiratory tract infections (URTI) by family medicine residents in order to identify educational interventions. Methods: Using purposive sampling of family medicine residents, semi-structured interviews were conducted until thematic saturation was reached. Interviews were coded into the domains of the Theoretical Domains Framework (TDF). Belief statements were created to characterize each domain and categorized as enablers or barriers to appropriate prescribing. Domains were plotted on the Behaviour Change Wheel (BCW) and intervention functions identified. Results:Twelve participants were interviewed. Nine domains of the TDF were relevant to antibiotic prescribing. Social influence was a prominent theme with the preceptor and patient being key influences on resident prescribing. Learning goals were also a key theme including the desire to strengthen independent clinical decision-making skills and improve antibiotic knowledge. Residents' beliefs about capabilities were challenged when faced with diagnostic uncertainty. Additional domains included: professional role; environmental context and resources; intentions; beliefs about consequences and capabilities, and knowledge. Using the BCW, nine intervention functions were identified to change antibiotic prescribing behaviour. Conclusion: This study found nine domains of the TDF were relevant to family medicine resident antibiotic prescribing for URTI. Nine intervention functions could be used to guide intervention design.

[Not Available]

Objectif

Faire la synthèse d’études de grande qualité sur 10 sujets, publiées en 2020, qui sont d’une grande pertinence pour la pratique des soins primaires.

Sélection des données probantes

La sélection des études s’est faite à la suite d’une surveillance systématique de la littérature scientifique par un groupe de professionnels de la santé en soins primaires. Les résumés de revues à fort impact et les EvidenceAlerts ont été dépouillés, de même que l’American College of Physicians Journal Club.

Message principal

Au nombre des articles en 2020 qui influenceront fort probablement la pratique des soins primaires figurent ceux portant sur les questions suivantes : l’antibioprophylaxie réduit-elle les infections maternelles à la suite d’un accouchement vaginal opératoire? Quel agent de deuxième intention après la metformine réduit les risques cardiovasculaires chez les patients diabétiques? La gabapentine est-elle efficace pour les troubles liés à la consommation d’alcool? Les bas de contention préviennent-ils la cellulite récurrente? Le jeûne intermittent est-il supérieur à des repas à heures régulières pour perdre du poids? La vitamine C ajoutée aux suppléments de fer augmente-t-elle plus l’hémoglobine que le fer seul? Les combinaisons d’antiacides et de lidocaïne sont-elles supérieures aux antiacides seuls pour la douleur épigastrique? La dapagliflozine améliore-t-elle les issues rénales et cardiovasculaires dans les cas de néphropathie chronique? L’empagliflozine améliore-t-elle les résultats cardiovasculaires chez les patients souffrant d’insuffisance cardiaque? Cinq sujets d’intérêt additionnels sont aussi passés brièvement en revue.

Conclusion

La recherche a produit en 2020 plusieurs études de grande qualité sur le diabète et les maladies cardiovasculaires, de même que sur divers autres problèmes pertinents en soins primaires, comme les accouchements vaginaux opératoires, les troubles liés à la consommation d’alcool, la perte pondérale et l’œdème chronique des jambes.

Masks for prevention of viral respiratory infections among health care workers and the public: PEER umbrella systematic review

OBJECTIVE

To determine the effect of mask use on viral respiratory infection risk.

DATA SOURCES

MEDLINE and the Cochrane Library.

STUDY SELECTION

Randomized controlled trials (RCTs) included in at least 1 published systematic review comparing the use of masks with a control group, either in community or health care settings, on the risk of viral respiratory infections.

SYNTHESIS

In total, 11 systematic reviews were included and 18 RCTs of 26 444 participants were found, 12 in the community and 6 in health care workers. Included studies had limitations and were deemed at high risk of bias. Overall, the use of masks in the community did not reduce the risk of influenza, confirmed viral respiratory infection, influenzalike illness, or any clinical respiratory infection. However, in the 2 trials that most closely aligned with mask use in real-life community settings, there was a significant risk reduction in influenzalike illness (risk ratio [RR] = 0.83; 95% CI 0.69 to 0.99). The use of masks in households with a sick contact was not associated with a significant infection risk reduction in any analysis, no matter if masks were used by the sick individual, the healthy family members, or both. In health care workers, surgical masks were superior to cloth masks for preventing influenzalike illness (RR = 0.12; 95% CI 0.02 to 0.98), and N95 masks were likely superior to surgical masks for preventing influenzalike illness (RR = 0.78; 95% CI 0.61 to 1.00) and any clinical respiratory infections (RR = 0.95; 95% CI 0.90 to 1.00).

CONCLUSION

This systematic review found limited evidence that the use of masks might reduce the risk of viral respiratory infections. In the community setting, a possible reduced risk of influenzalike illness was found among mask users. In health care workers, the results show no difference between N95 masks and surgical masks on the risk of confirmed influenza or other confirmed viral respiratory infections, although possible benefits from N95 masks were found for preventing influenzalike illness or other clinical respiratory infections. Surgical masks might be superior to cloth masks but data are limited to 1 trial.

PEER umbrella systematic review of systematic reviews: Management of osteoarthritis in primary care

OBJECTIVE

To determine how many patients with chronic osteoarthritis pain respond to various non-surgical treatments.

DATA SOURCES

PubMed and the Cochrane Library.

STUDY SELECTION

Published systematic reviews of randomized controlled trials (RCTs) that included meta-analysis of responder outcomes for at least 1 of the following interventions were included: acetaminophen, oral nonsteroidal anti-inflammatory drugs (NSAIDs), topical NSAIDs, serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants, cannabinoids, counseling, exercise, platelet-rich plasma, viscosupplementation, glucosamine, chondroitin, intra-articular corticosteroids, rubefacients, or opioids.

SYNTHESIS

In total, 235 systematic reviews were included. Owing to limited reporting of responder meta-analyses, a post hoc decision was made to evaluate individual RCTs with responder analysis within the included systematic reviews. New meta-analyses were performed where possible. A total of 155 RCTs were included. Interventions that led to more patients attaining meaningful pain relief compared with control included exercise (risk ratio [RR] of 2.36; 95% CI 1.79 to 3.12), intra-articular corticosteroids (RR = 1.74; 95% CI 1.15 to 2.62), SNRIs (RR = 1.53; 95% CI 1.25 to 1.87), oral NSAIDs (RR = 1.44; 95% CI 1.36 to 1.52), glucosamine (RR = 1.33; 95% CI 1.02 to 1.74), topical NSAIDs (RR = 1.27; 95% CI 1.16 to 1.38), chondroitin (RR = 1.26; 95% CI 1.13 to 1.41), viscosupplementation (RR = 1.22; 95% CI 1.12 to 1.33), and opioids (RR = 1.16; 95% CI 1.02 to 1.32). Preplanned subgroup analysis demonstrated no effect with glucosamine, chondroitin, or viscosupplementation in studies that were only publicly funded. When trials longer than 4 weeks were analyzed, the benefits of opioids were not statistically significant.

CONCLUSION

Interventions that provide meaningful relief for chronic osteoarthritis pain might include exercise, intra-articular corticosteroids, SNRIs, oral and topical NSAIDs, glucosamine, chondroitin, viscosupplementation, and opioids. However, funding of studies and length of treatment are important considerations in interpreting these data.

Top studies relevant to primary care from 2018: From PEER

OBJECTIVE

To summarize high-quality studies for 10 topics from 2018 that have strong relevance to primary care practice.

QUALITY OF EVIDENCE

Study selection involved routine literature surveillance by a group of primary care health professionals. This included screening abstracts of important journals and Evidence Alerts, as well as searching ACP Journal Club.

MAIN MESSAGE

Topics of the 2018 articles include whether low-dose acetylsalicylic acid improves health outcomes like cardiovascular disease (CVD); whether a low-carbohydrate diet is better than a low-fat diet for weight loss (and whether genetics matter); whether vaginal estradiol is superior to placebo for vulvovaginal symptoms of menopause; whether opioid management is better than nonopioid management for chronic back or osteoarthritis pain; whether additional water intake will decrease recurrent urinary tract infections; whether omega-3 fatty acids prevent CVD or reduce dry eyes; whether the new drug icosapent improves CVD; whether bath additives help eczema; whether acetaminophen can prevent recurrent febrile seizures; and recommendations for glycemic targets in diabetes based on reviews of evidence and other guidelines. Five "runner-up" studies are also briefly reviewed.

CONCLUSION

Research from 2018 produced several high-quality studies in CVD but also spanned the breadth of primary care including pediatrics, women's health, and pain management, among other areas.

[Not Available]

Objectif

Résumer des études de qualité supérieure sur 10 sujets en 2018 qui sont étroitement en rapport avec la pratique des soins primaires.

Qualité des données

Pour choisir les études, un groupe de professionnels des soins de santé primaires a exercé une surveillance systématique des publications scientifiques, notamment par un examen des résumés de revues réputées et une recension des Evidence Alerts et dans l’ACP Journal Club.

Message principal

Les questions soulevées dans les articles de 2018 cherchaient à savoir : si l’acide acétylsalicylique à faible dose améliore les issues en matière de santé telles que les maladies cardiovasculaires (MCV); si un régime faible en glucides est meilleur qu’un régime faible en gras pour perdre du poids (ou la génétique est-elle un facteur?); si l’estradiol vaginal est supérieur à un placebo pour les symptômes vulvovaginaux de la ménopause; si la prise en charge de la lombalgie et de la douleur arthritique chronique est plus efficace avec des opioïdes ou des agents sans opioïde; si la consommation d’une plus grande quantité d’eau diminuera la récurrence des infections des voies urinaires; si les acides gras oméga-3 préviennent les MCV ou la sécheresse oculaire; si le nouveau médicament à base d’acide eicosapentaénoïque a un effet bénéfique sur les MCV; si les additifs pour le bain aident dans les cas d’eczéma; si l’acétaminophène peut prévenir les convulsions fébriles; et quelles sont les recommandations de valeurs cibles de la glycémie en fonction de la revue des données probantes et d’autres lignes directrices? Cinq autres sujets dans la liste par ordre d’importance ont aussi fait l’objet d’une brève revue.

Conclusion

En 2018, la recherche a produit des études de grande qualité sur les MDC, mais les sujets abordés ont aussi porté sur des éléments qui s’inscrivent dans la vaste portée des soins primaires, comme, entre autres, la pédiatrie, la santé des femmes et le contrôle de la douleur.

Oral calcitriol versus oral alfacalcidol for the treatment of secondary hyperparathyroidism in patients receiving hemodialysis: a randomized, crossover trial

BACKGROUND

Secondary hyperparathyroidism is a common complication in patients with chronic kidney disease and treatment with vitamin D analogues is a mainstay of therapy. Although oral calcitriol and alfacalcidol are used extensively in Canada, there is little published data comparing equal doses of these agents.

OBJECTIVES

To compare the effect of equal doses of oral calcitriol and alfacalcidol on intact parathyroid hormone concentrations (iPTH) in the treatment of secondary hyperparathyroidism due to chronic kidney disease. Secondary endpoints included serum 1,25-dihydroxyvitamin D3, calcium and phosphate concentrations, achievement of target iPTH concentrations, and need for phosphate binder dose increases.

METHODS

Five adult hemodialysis subjects who were naA ve to vitamin D analogues and had iPTH concentrations > or = 20 pmol/L were enrolled in a prospective, randomized 16-week crossover pilot study. Subjects were randomized to either oral calcitriol or oral alfacalcidol 0.75 mcg three times weekly for six weeks. After a four-week washout period, patients were crossed over to the alternate drug for six weeks.

RESULTS

Oral calcitriol significantly suppressed iPTH after six weeks of therapy (p=0.003), while no significant change in iPTH was observed with oral alfacalcidol.

CONCLUSIONS

This small randomized crossover study provides preliminary evidence that equal doses of oral alfacalcidol and calcitriol may demonstrate differences in iPTH suppression during the first six weeks in dialysis patients treated for secondary hyperparathyroidism. Further comparative trials are required to confirm this finding and to determine whether important differences in parathyroid hormone suppression exist between oral calcitriol and alfacalcidol beyond the six-week period. Key words: Vitamin D analogues, alfacalcidol, calcitriol, secondary hyperparathyroidism, renal dialysis.

Definition, evaluation, and classification of renal osteodystrophy: a position statement from Kidney Disease: Improving Global Outcomes (KDIGO)

Disturbances in mineral and bone metabolism are prevalent in chronic kidney disease (CKD) and are an important cause of morbidity, decreased quality of life, and extraskeletal calcification that have been associated with increased cardiovascular mortality. These disturbances have traditionally been termed renal osteodystrophy and classified based on bone biopsy. Kidney Disease: Improving Global Outcomes (KDIGO) sponsored a Controversies Conference on Renal Osteodystrophy to (1) develop a clear, clinically relevant, and internationally acceptable definition and classification system, (2) develop a consensus for bone biopsy evaluation and classification, and (3) evaluate laboratory and imaging markers for the clinical assessment of patients with CKD. It is recommended that (1) the term renal osteodystrophy be used exclusively to define alterations in bone morphology associated with CKD, which can be further assessed by histomorphometry, and the results reported based on a unified classification system that includes parameters of turnover, mineralization, and volume, and (2) the term CKD-Mineral and Bone Disorder (CKD-MBD) be used to describe a broader clinical syndrome that develops as a systemic disorder of mineral and bone metabolism due to CKD, which is manifested by abnormalities in bone and mineral metabolism and/or extra-skeletal calcification. The international adoption of these recommendations will greatly enhance communication, facilitate clinical decision-making, and promote the evolution of evidence-based clinical practice guidelines worldwide.

Early manifestations of "sick euthyroid" syndrome in patients with compensated chronic heart failure

BACKGROUND

A "sick euthyroid" syndrome occurs in patients with severe decompensated chronic heart failure (CHF) and other chronic illnesses and is related to adverse prognosis, but it has not been described in patients with compensated CHF. The aim of this study was to determine whether manifestations of the sick euthyroid syndrome occur in patients with compensated CHF caused by ischemic heart disease.

METHODS AND RESULTS

Thyroid hormonal responses to thyrotropin-releasing hormone (TRH) stimulation were compared in 8 patients with New York Heart Association class I/II CHF considered secondary to ischemic heart disease and 7 control patients after serial 10-minute blood sampling over 3-hour periods. Secretory dynamics of TRH-induced thyroid-stimulating hormone (TSH) release were compared by using deconvolution analysis. Changes in serum thyroxine (T4), triiodothyronine (T3), reverse T3 (rT3), and rT3/T4 concentration ratios were compared. Patients with CHF had lower baseline serum T3 concentrations (P <.001), with lower maximum serum T(3) (P <.01) and higher maximum serum rT(3) (P <.05) concentrations after TRH stimulation but similar estimated TRH-induced TSH secretory burst amplitude, mass, and 3-hour production rates, compared with control patients.

CONCLUSIONS

Patients with compensated CHF display the derangements in thyroid hormone metabolism of impaired peripheral conversion of T4 and T3 and increased production of rT(3) in the presence of normal dynamic function of the hypothalamic-pituitary-thyroid axis, which are consistent with early manifestations of a sick euthyroid state.

Acute tubulointerstitial nephritis attributable to indinavir therapy

Indinavir sulfate has been reported to cause asymptomatic crystalluria and nephrolithiasis in patients with human immunodeficiency virus (HIV) infection. Patients taking indinavir may present with asymptomatic crystalluria, nephrolithiasis with frank renal colic and obstruction, flank pain in the absence of nephrolithiasis, and dysuria or urgency. Asymptomatic crystalluria has been described as benign. Discontinuation of the drug has not been recommended in the absence of nephrolithiasis. We report two HIV-positive patients receiving indinavir who developed acute interstitial nephritis with foreign body giant cell reaction on renal biopsies. Both patients had asymptomatic crystalluria, although crystals were associated with clumps of white blood cells (WBCs) on urinalysis in one patient. Both cases show that the inflammatory response was significant enough to lead to tubular injury and acute renal impairment. Our findings suggest that asymptomatic crystalluria attributable to indinavir may illicit an inflammatory response with acute renal insufficiency, warranting monitoring of renal function, especially in patients with crystalluria.

Proteolytic activation of cholera toxin and Escherichia coli labile toxin by entry into host epithelial cells. Signal transduction by a protease-resistant toxin variant

Cholera and Escherichia coli heat-labile toxins (CT and LT) require proteolysis of a peptide loop connecting two major domains of their enzymatic A subunits for maximal activity (termed "nicking"). To test whether host intestinal epithelial cells may supply the necessary protease, recombinant rCT and rLT and a protease-resistant mutant CTR192H were prepared. Toxin action was assessed as a Cl- secretory response (Isc) elicited from monolayers of polarized human epithelial T84 cells. When applied to apical cell surfaces, wild type toxins elicited a brisk increase in Isc (80 microA/cm2). Isc was reduced 2-fold, however, when toxins were applied to basolateral membranes. Pretreatment of wild type toxins with trypsin in vitro restored the "basolateral" secretory responses to "apical" levels. Toxin entry into T84 cells via apical but not basolateral membranes led to nicking of the A subunit by a serine-type protease. T84 cells, however, did not nick CTR192H, and the secretory response elicited by CTR192H remained attenuated even when applied to apical membranes. Thus, T84 cells express a serine-type protease(s) fully sufficient for activating the A subunits of CT and LT. The protease, however, is only accessible for activation when the toxin enters the cell via the apical membrane.

Targeting of cholera toxin and Escherichia coli heat labile toxin in polarized epithelia: role of COOH-terminal KDEL

Vibrio cholerae and Escherichia coli heat labile toxins (CT and LT) elicit a secretory response from intestinal epithelia by binding apical receptors (ganglioside GM1) and subsequently activating basolateral effectors (adenylate cyclase). We have recently proposed that signal transduction in polarized cells may require transcytosis of toxin-containing membranes (Lencer, W. I., G. Strohmeier, S. Moe, S. L. Carlson, C. T. Constable, and J. L. Madara. 1995. Proc. Natl. Acad. Sci. USA. 92:10094-10098). Targeting of CT into this pathway depends initially on binding of toxin B subunits to GM1 at the cell surface. The anatomical compartments in which subsequent steps of CT processing occur are less clearly defined. However, the enzymatically active A subunit of CT contains the ER retention signal KDEL (RDEL in LT). Thus if the KDEL motif were required for normal CT trafficking, movement of CT from the Golgi to ER would be implied. To test this idea, recombinant wild-type (wt) and mutant CT and LT were prepared. The COOH-terminal KDEL sequence in CT was replaced by seven unrelated amino acids: LEDERAS. In LT, a single point mutation replacing leucine with valine in RDEL was made. Wt and mutant toxins displayed similar enzymatic activities and binding affinities to GM1 immobilized on plastic. Biologic activity of recombinant toxins was assessed as a Cl- secretory response elicited from the polarized human epithelial cell line T84 using standard electrophysiologic techniques. Mutations in K(R)DEL of both CT and LT delayed the time course of toxin-induced Cl- secretion. At T1/2, dose dependencies for K(R)DEL-mutant toxins were increased > or = 10-fold. KDEL-mutants displayed differentially greater temperature sensitivity. In direct concordance with a slower rate of signal transduction. KDEL-mutants were trafficked to the basolateral membrane more slowly than wt CT (assessed by selective cell surface biotinylation as transcytosis of B subunit). Mutation in K(R)DEL had no effect on the rate of toxin endocytosis. These data provide evidence that CT and LT interact directly with endogenous KDEL-receptors and imply that both toxins may require retrograde movement through Golgi cisternae and ER for efficient and maximal biologic activity.

Transcytosis of cholera toxin subunits across model human intestinal epithelia

Cholera toxin (CT) elicits a massive secretory response from intestinal epithelia by binding apical receptors (ganglioside GM1) and ultimately activating basolateral effectors (adenylate cyclase). The mechanism of signal transduction from apical to basolateral membrane, however, remains undefined. We have previously shown that CT action on the polarized human intestinal epithelial cell line T84 requires endocytosis and processing in multiple intracellular compartments. Our aim in the present study was to test the hypothesis that CT may actually move to its site of action on the basolateral membrane by vesicular traffic. After binding apical receptors, CT entered basolaterally directed transcytotic vesicles. Both CT B subunits and to a lesser extent CT A subunits were delivered intact to the serosal surface of the basolateral membrane. The toxin did not traverse the monolayer by diffusion through intercellular junctions. Transcytosis of CT B subunits displayed nearly identical time course and temperature dependency with that of CT-induced Cl- secretion--suggesting the two may be related. These data identify a mechanism that may explain the link between the toxin's apical receptor and basolateral effector.

Signal transduction by cholera toxin: processing in vesicular compartments does not require acidification

In the polarized human intestinal epithelial cell line T84, signal transduction by cholera toxin (CT) follows a complex series of events in which CT enters the apical endosome and moves through multiple vesicular compartments before it activates adenylate cyclase. As with processing of many other surface ligands, it has been suggested that CT must enter acidic vesicles to exert its downstream effects. To determine if intravesicular pH may regulate signal transduction by CT, we examined the cAMP-dependent Cl- secretory response [short-circuit current (Isc)] to CT in T84 cell monolayers treated with chloroquine (500 microM), methylamine (50 mM), NH4Cl (10 mM), nigericin (4 microM), or bafilomycin A1 (1 microM). Each of these reagents collapsed intravesicular pH gradients as confirmed by accumulation of acridine orange within subcellular compartments of living T84 cells imaged by confocal epifluorescence microscopy. Both acidotropic amines and nigericin inhibited the cAMP-dependent Cl secretory response in T84 cells. However, none of these reagents specifically affected adenylate cyclase itself or coupling of adenylate cyclase with the heterotrimeric guanosinetriphosphatase Gs as judged by the secretory response to the adenosine 3',5'-cyclic monophosphate (cAMP) agonists vasoactive intestinal peptide (VIP), forskolin, or 8-bromo-cAMP. In vitro enzyme-linked immunosorbent assay showed that CT binding to ganglioside GM1 was not dependent on pH between 5.0 and 10. Maximal Isc elicited by apical CT relative to maximal Isc elicited by VIP was not affected by pretreatment with chloroquine, methylamine, NH4Cl, or bafilomycin AI. Nigericin was the only reagent to inhibit CT-induced Isc (5 +/- 2% maximal response to VIP). The data indicate that low intravesicular pH will have little or no effect on CT association with its membrane receptor GM1, or on subsequent processing/signal transduction events.

Entry of cholera toxin into polarized human intestinal epithelial cells. Identification of an early brefeldin A sensitive event required for A1-peptide generation

The effect of brefeldin-A (BFA), a reversible inhibitor of vesicular transport, on cholera toxin (CT)-induced Cl- secretion (Isc) was examined in the polarized human intestinal cell line, T84. Pretreatment of T84 monolayers with 5 microM BFA reversibly inhibited Isc in response to apical or basolateral addition of 120 nM CT (2.4 +/- 0.5 vs. 68 +/- 3 microA/cm2, n = 5). In contrast, BFA did not inhibit Isc responses to the cAMP agonist VIP (63 +/- 7 microA/cm2). BFA had no effect on cell surface binding and endocytosis of a functional fluorescent CT analog or on the dose dependency of CT induced 32P-NAD ribosylation of Gs alpha in vitro. In contrast, BFA completely inhibited (> 95%) the ability of T84 cells to reduce CT to the enzymatically active A1-peptide. BFA had to be added within the first 10 min of CT exposure to inhibit CT-elicited Isc. The early BFA-sensitive step occurred before a temperature-sensitive step essential for apical CT action. These studies show that sequential steps are required for a biological response to apical CT: (a) binding to cell surfaces and rapid endocytosis; (b) early, BFA-sensitive vesicular transport essential for reduction of the A1-peptide; and (c) subsequent temperature-sensitive translocation of a signal (the A1-peptide or possibly ADP-ribose-Gs alpha) to the basolateral domain.