Radiation Therapy Sensitizes Head-and-Neck Cancer Cells to Killing by Chimeric Antigen Receptor (CAR)-NK Cells Targeting CD70

PURPOSE/OBJECTIVE(S)

CAR-T cell therapy is limited by toxicity, high cost, logistical manufacturing issues in the autologous setting and risk of GVHD in the allogeneic setting. Substitution of T cells with NK cells opens the possibility for an allogeneic off-the-shelf product with a better safety profile. However, the inadequate efficacy of CAR-NK cells against solid tumors can be extrapolated from experience with CAR-T cells. There is limited but promising preclinical evidence that radiation therapy (RT) enhances CAR-T cell tumoricidal activity against solid tumors. However, there is no data examining the potential synergy between RT and CAR-NK cell therapy.

MATERIALS/METHODS

We engineered CAR-NK cells with CD27 receptor as extracellular domain to target its natural ligand CD70, which is overexpressed in head-and-neck cancers (HNSCC). CAR-NK cell killing was assessed real-time through xCELLigence cytotoxicity assays. CD70+ OQ01 human HNSCCs were used for most experiments. FaDu is a CD70- HNSCC (negative ctrl). UMRC3 is a CD70+ kidney cancer cell line (positive ctrl). CD70 expression pre- and post-RT was assessed by flow cytometry and Western blot. Ionizing RT was compared at 5 doses: 0, 1.75, 3.5, 7, and 14 Gy. A single dose of 3.5 Gy was used for most experiments. Post-radiation effects were generally assessed at 3 days or 9 days post-RT. Intracellular staining was used to assess NK cell expression of IFN-γ, CD107a, and TNF-α by flow cytometry. CD27/CD70 interaction blockade was through α-CD27 pre-treatment of CAR-NK cells.

RESULTS

OQ01 HNSCCs heterogeneously express CD70 and are killed by CD70 CAR-NK cells in vitro. Pre-conditioning low-dose RT of 3.5 Gy applied to OQ01 HNSCCs 3 days prior to coculture with NK cells enhances CD70 CAR-NK cell killing, with ∼30% increased cytotoxicity against the tumor cells. Low-dose RT by itself did not induce acute cytolysis. As a possible mechanism for the increased sensitivity of irradiated OQ01 cells to CD70 CAR-NK cells, we found that RT enhances CD70 expression among HNSCCs in a dose-dependent manner. There was no increase in NK cell expression of IFN-γ, CD107a, and TNF-α with exposure to irradiated target cells. CD27/CD70 blockade does not solely abrogate RT-induced sensitization toward CAR-NK cell killing. Despite RT induction of transient increased expression of CD70, which normalizes by 9 days post-RT, there is persistent increase in RT-synergized target cell killing even at this later timepoint. Thus, altogether, RT sensitizes CD70-expressing HNSCC cells to CAR-NK cell killing in vitro.

CONCLUSION

This work represents the first preclinical study to identify the synergy of RT and CAR-NK cell therapy in solid tumors and is the first demonstration of CAR-NK cell activity against human HNSCCs. We show significantly enhanced potency of CAR-NK cells against irradiated tumor cells in vitro. Collectively, this research will be vital to guide efforts expanding into other target antigens and tumor types.

AB0732 Abatacept as therapy option in systemic sclerosis (SSc) patients after years of Grazer- protocol treatment- Our Experience

Background

Previous studies have provided evidence that T cells may play a significant role in the pathogenesis of systemic sclerosis (SSc) and observational studies reported that Abatacept, which interferes with T cells activation, appeared to be safe and effective in SSc-patients with skin and muscle involvement. So far, there was no significant effective treatment for SSC-ILD. We have recently demonstrated the effectiveness of intensified –RTX- long term treatment (“Grazerprotocol” with 500 mg RTX in week 0 and 2, every 3 months +/- MMF) in SSc patients with severe organ involvement and/or progressive form non responding to methotrexate or cyclophosphamide. However, no data are available concerning how long Patients with a stable disease need to be treated. B-cell-depletion therapy over years for SSC in remission might represent a risk factor for infections. Additionally, the parenteral administration is associated with an increase in health care and patients are bound to regular hospital visits, which is a limiting factor for life quality.

Objectives

We aimed to investigate if subcutaneous Abatacept could be used as a maintenance treatment in SSc-patients reaching a stable disease activity after a treatment with RTX administered according to our Grazer protocol over several years.

Methods

In this retrospective analysis, we retrieved data from 20 patients who fulfilled the diagnosis criteria for systemic sclerosis (SSc) according to the European League Against Rheumatism Scleroderma Trial and Research standards, who started a treatment with abatacept (ABA) after years of 500 mg RTX therapy every three months +/- MMF (Grazer protocol). The following clinical parameter were evaluated: modified Rodnan Skin Score (mRSS), Systemic Sclerosis Activity Score (SScAS), Systemic Sclerosis Severity Score (SScSS) and lung diffusing capacity for carbon monoxide (DLCO). Lab parameters like IgG, ANA, ENA and inflammation parameters were routinely assessed. Clinical data from baseline visit (BSL) (before ABA treatment start) and follow-up visit (FU) (after 6 months of treatment) were collected.

Results

We included 20 SSc patients in this retrospective analysis who changed from RTX to Abatacept. The majority were female (n=16; 94.1%), with a mean age ±SD of 54.8 years ±11 and an average disease duration of 7.7 years ±4.5. In 17.9% (n=4) treatment needed to be stopped due to disease flare after three months (lung n=2, skin and tendons n=2).

However, interestingly, Abatacept further decreased significantly mRSS between baseline visit and follow-up visit regarding the affected skin of the fingers. Thus, the mRSS went from 3.9±3.4 to 2.5±1.8 (p<0.05). As expected, no significant difference in the EUSTAR-SScAS, or ScSS or DLCO was found. No infections were observed during the abatacept follow-up period and Immunoglobulins remained within the normal range.

Conclusion

Abatacept might be a feasible option as a maintenance therapy after intensive immunomodulation with RTX and may give our patients the possibility to further improve their quality of life.

The fact that 4 patients experienced a relapse after switching to Abatacept warrants further studies to find prognostic factors.

Disclosure of Interests

None declared

Mythes et variations culturelles autour du cancer dans les pays du bassin méditerranéen

L’incidence du cancer et la mortalité par cette maladie sont en nette progression dans le monde, et plus particulièrement dans les pays en voie de développement, incluant les pays du Moyen-Orient et de l’Afrique du Nord. Les barrières au contrôle du cancer dans ces régions sont d’ordre économique et organisationnel mais aussi dues aux causes culturelles associées à l’ignorance, aux mythes et aux tabous liés au cancer. Il existe plusieurs raisons qui ont stigmatisé le cancer ; la plupart des personnes dans ces régions continuent à considérer que le cancer est une maladie fatale à tous les coups, qu’il peut être contagieux. Il est même parfois considéré comme une punition. Les paroles de patients qui évoquent ces stigmates et ces perceptions sont rapportées. Le rôle de la famille et de la spiritualité est évoqué. Ces mythes et tabous sont un continuel défi pour le contrôle du cancer : ils entraînent un effet contraire aux efforts de sensibilisation et de prévention du cancer. D’où l’objectif n° 5 de la Déclaration universelle de l’UICC de faire disparaître les effets néfastes des mythes et des stigmates. Après avoir passé en revue plusieurs exemples de mythes et de tabous rencontrés dans la pratique, nous rapportons quelques leçons apprises et utiles dans la lutte contre le cancer dans les pays du Moyen- Orient et du nord de l’Afrique.

Ibrutinib modulates the immunosuppressive CLL microenvironment through STAT3-mediated suppression of regulatory B-cell function and inhibition of the PD-1/PD-L1 pathway

Ibrutinib, a covalent inhibitor of Bruton Tyrosine Kinase (BTK), is approved for treatment of patients with relapsed/refractory or treatment-naïve chronic lymphocytic leukemia (CLL). Besides directly inhibiting BTK, ibrutinib possesses immunomodulatory properties through targeting multiple signaling pathways. Understanding how this ancillary property of ibrutinib modifies the CLL microenvironment is crucial for further exploration of immune responses in this disease and devising future combination therapies. Here, we investigated the mechanisms underlying the immunomodulatory properties of ibrutinib. In peripheral blood samples collected prospectively from CLL patients treated with ibrutinib monotherapy, we observed selective and durable downregulation of PD-L1 on CLL cells by 3 months post-treatment. Further analysis showed that this effect was mediated through inhibition of the constitutively active signal transducer and activator of transcription 3 (STAT3) in CLL cells. Similar downregulation of PD-1 was observed in CD4+ and CD8+ T cells. We also demonstrated reduced interleukin (IL)-10 production by CLL cells in patients receiving ibrutinib, which was also linked to suppression of STAT3 phosphorylation. Taken together, these findings provide a mechanistic basis for immunomodulation by ibrutinib through inhibition of the STAT3 pathway, critical in inducing and sustaining tumor immune tolerance. The data also merit testing of combination treatments combining ibrutinib with agents capable of augmenting its immunomodulatory effects.

Is percutaneous medial hamstring myofascial lengthening as anatomically effective and safe as the open procedure?

BACKGROUND

Medial hamstring fractional lengthening is commonly performed in children with cerebral palsy (CP) to decrease contracture and/or to improve gait. Percutaneous procedures are gaining more and more popularity, even in the paediatric population, with equivocal results. The purpose of this paper was to determine the efficacy and safety of percutaneous medial hamstring myofascial lengthening (PHL).

METHODS

This is a prospective randomised controlled trial including 31 knees from 18 consecutive patients with CP scheduled for medial hamstring lengthening in the setting of multilevel tendon lengthening procedures in a university hospital. Other concomitant lower extremity surgeries were not exclusionary. A first paediatric orthopaedic surgeon executes the PHL at one level, as recently described in the literature. Another surgeon opens and extends the wound to explore what had been cut during the PHL and completes fractional lengthening (OHL) of both the semimembranosus (SM) and semitendinosus (ST) when possible. Popliteal angle (PA) was assessed by a third surgeon immediately before PHL, after PHL and then after OHL, using a goniometer in a standardised reproducible manner. All three surgeons were blinded to the others' findings. Primary endpoints included ease of performing PHL, the percentage of tendon-fascia/ muscle portion sectioned percutaneously and improvement of PA. Comparison between improvement of PA after PHL and OHL was done using a paired t-test with a 95% confidence interval.

RESULTS

The first surgeon was at ease in palpating and identifying the semimembranosus tendon before PHL in ten knees only. PHL led to an undesirable cut of the semimembranosus muscle fibres to more than 50% of the muscle section area in eight cases (<50% in 23 cases, between 50% and 75% in eight cases), and of the semitendinosus muscle fibres to more than 50% in all cases (complete rupture in six cases, more than 75% in eight cases and approximately 50% in 17 cases). Mean PA measured 52° pre-operatively and decreased to 40° after PHL. After OHL, the PA averaged 22°. There was a significant difference between the PA value after PHL (M = 40, SD = 11.8) and the PA value after OHL (M = 22, SD = 8.7), p < 0.0001. The gain in PA did not correlate with the extent of semimembranosus muscle divided (p = 0.38) nor with the extent of semitendinosus muscle divided (p = 0.35). No major iatrogenic neurovascular injury was observed.

CONCLUSIONS

To the authors' knowledge, this is the first prospective study concerning the anatomic effects of PHL. Although it is a quick procedure, it is often associated with difficulty by the operating surgeon to identify and evaluate what should be cut percutaneously, leading to abusive injury of the muscle itself rather than the fascia alone. In addition, the gain in PA is statistically less following PHL than following OHL despite undesirable extensive muscle injury following PHL. This may be due to the multiple fascial cuts (fractional lengthening) usually performed in OHL.

Ethical issues in the geriatric patient with advanced cancer 'living to the end'

Cancer incidence will increase as the population ages; there will be a 50% increase in new cancer cases over the next 20 years, and the biggest rates of increase will occur in the developing world. Owing to technical advances in the care of critical illness, as it is the case in elderly people with advanced cancer, physicians, patients and families are often confronted with ambiguous circumstances in which medical advances may inadvertently prolong suffering and the dying process rather than bring healing and recovery. In this review of the ethical issues confronting physicians who care for patients with advanced life-limiting illnesses like cancer, a philosophical debate continues in the medical community regarding the rightness or wrongness of certain actions (e.g. physician-assisted death, euthanasia), while at the same time there is a strong desire to find a common ground for moral discourse that could guide medical decision-making in this difficult period in the lives of our patients. We will discuss how a good palliative care can be an alternative to these ethical dilemmas. Although some issues (e.g. the role of physician-assisted death in addressing suffering) remain very controversial, there is much common ground based on the application of the four major principles of medical ethics, no malfeasance, beneficence, autonomy and justice. Thus, the physician's primary commitment must always be the patient's welfare and best interests, whether the physician is treating illness or helping patients to cope with illness, disability and death. A key skill here is the communication of bad news and to negotiate a treatment plan that is acceptable to the patient, the family and the healthcare team. Attention to psychosocial issues demands involvement of the patients and their families as partners. Physicians should be sensitive to the range of psychosocial distress and social disruption common to dying patients and their families. Spiritual issues often come to the fore. An interdisciplinary healthcare team can help in these areas. The goals of this review are to raise the awareness of doctors, nurses and other members of the healthcare team to the important ethical issues that must be addressed in providing medical care to elderly patients with advanced cancer; and also to encourage members of the healthcare team to take the ethical issues seriously so that we can improve the circumstances of a vulnerable group of patients-the elderly patients with cancer.

Multidisciplinary care team for cancer patients and its implementation in several Middle Eastern countries

This article introduces palliative care to cancer patients in Middle Eastern countries. It considers the importance of the multidisciplinary team in providing an adequate service to the patient and his/her family. It provides views of professionals from the various countries with regard to the role of the nurse in such teams; whereby the three elements of palliative care nursing entail: 1. Working directly with patients and families; 2. Working with other health and social care professionals to network and co-ordinate services; and 3. working at an organizational level to plan, develop and manage service provision in local, regional and national settings. This article also details the challenges that nurses face in the Middle East and outlines the preferable ways to overcome such challenges. The latter include more focused educational activities at the undergraduate and graduate levels and continuous clinical training throughout their work as palliative care nurse specialists.

Pneumorachis after cocaine sniffing

Air in the epidural space is called pneumorachis. The usual mechanism of pneumorachis is air diffusion from the mediastinal tissue layers through the inter-vertebral foramen. Alternatively, air can diffuse directly after spine traumas (e.g., blunt deceleration with vertebral dislocation) or medical procedures. Several mechanisms could explain pneumomediastinum and pneumorachis after cocaine sniffing. Passive apnea and/or cough that occur after sniffing can cause intra alveolar hyper-pressure, which is responsible for alveolar rupture and air diffusion. Another mechanism is alveolar wall fragility and rupture induced by repeated cocaine sniffing, in turn causing air diffusion to the mediastinum, sub-cutaneous tissues and the epidural space. The diagnosis is usually made on Chest tomography scan. Management consists in close monitoring in the intensive care unit to detect aggravation of pneumomediastinum and pneumorachis, which would require surgical management. Supplemental nasal oxygen can be given to accelerate nitrogen washout. We present a case of a 28 years old male who presented to the emergency department for chest pain directly after sniffing cocaine. A computed tomography scan of the chest showed pneumomediastinum, pneumorachis and sub-cutaneous emphysema. The patient was admitted for 24 h: after that delay, surveillance chest tomodensitometry showed stability, and he could be discharged without further treatment.

Promoting new approaches for cancer care in the Middle East

Cancer is now the fastest growing killing disease in the Middle East. Accordingly, there is an urgent need to train local health professionals: oncologists, palliative care experts, oncology nurses, psychologists, along with social workers, physiotherapists and spiritual counselors on strategies for early detection, curative therapies and palliation. Professionals in the region, along with the public, need to convince medical administrators, regulators and policymakers about investing in education and training of YOUNG professionals, as well as those with already proven experience in cancer care. Training is the basis for any future cancer care program, which aims at the integration of palliative care practices into standard oncology care across the trajectory of the illness.

[Bronchopericardial fistula treatment by a metallic stent]

INTRODUCTION

Bronchopericardial fistula is a rare condition leading to pneumopericardium. This medical condition is often related to neoplastic disease, or a complication of surgical interventions. The treatment approach depends on both the etiology and the clinical presentation. In stable patients, pericardial drain insertion and/or surgical resection of the fistula are considered options for persistent cases. We present the case of a bronchopericardial fistula treated by placement of an endobronchial stent.

CASE PRESENTATION

A 64-year-old man operated on for lung cancer had a recurrence treated with radiation and chemotherapy. A pneumopericadium was discovered when he presented with a new onset of atrial fibrillation. Bronchoscopy revealed a fistula tract. Pericardial drainage was persistent and did not improve the clinical situation. The poor health status of the patient contraindicated surgery and an alternative therapeutic approach with endobronchial stent placement was undertaken. The fistula sealed immediately, the pericardial drain could be removed removed and the patient was able to be discharged from hospital.

CONCLUSION

Endobronchial stenting should be considered as a potential treatment option in patients with pneumopericardium secondary to bronchopericadial fistula, particularly where a non-surgical is required.

Palliative cancer care in Middle Eastern countries: accomplishments and challenges

BACKGROUND

In larger parts of the Middle East palliative care is still misunderstood among health professionals, cancer patients and the public at large. One reason to that is because the term does not obviously communicate the intent of this clinical discipline, which is lending better quality of life while combating cancer. Further, culture, tradition and religion have contributed to this misgiving and confusion especially at the terminal stage of the disease.

METHODS

The Middle East Cancer Consortium jointly with the American Society of Clinical Oncology, the American Oncology Nursing Society, the San Diego Hospice Center for Palliative Medicine and the Children's Hospital & Clinics of Minnesota initiated a series of training courses and workshops in the Middle East to provide updated training to physicians, nurses, social workers and psychologists from throughout the region with basic concepts of palliative care and pain managements in adults and children cancers.

RESULTS

During the past 6 years hundreds of professionals took part in these educational and training activities, thereby creating the core of trained caregivers who start to make the change in their individual countries.

CONCLUSIONS

The outcome of consecutive training activities can overcome geopolitical instabilities, and yield a genuine change in approach of both regulators, medical administrators, medical staff and the public; as to the important contribution of palliative care services to the welfare of the patient and his/her family.

[Aggressive fibromatosis (desmoid tumor) : A rare differential diagnosis of metastasis of renal cell carcinoma]

We report the case of a 65-year-old woman with an aggressive fibromatosis of the rectus abdominis muscle suspicious for a metastasis of renal cell carcinoma after tumor nephrectomy 3 years previously. Aggressive fibromatoses (desmoid tumors) are rare semimalignant tumors of the connective tissue with local infiltration and destruction of tissue. Complete resection is essential to avoid tumor relapse. Aggressive fibromatosis must be considered in the differential diagnosis of renal cell carcinoma metastasis. Complete resection and subsequent radiotherapy seem to be the therapy of choice.

Healthcare and workloss costs associated with patients with persistent asthma in a privately insured population

OBJECTIVE

The objective of this study was to estimate annual healthcare and workloss costs of patients with persistent asthma by severity.

METHODS

A persistent asthma patient sample (<65 years) was selected from an employer claims database. Asthma persistence and severity were determined by a novel algorithm based on Health Plan Employer Data and Information Set criteria, Leidy's Reliever and Oral Steroid Method, and Global Initiative for Asthma guidelines. Healthcare costs were compared between asthma patients and demographically matched controls and by asthma severity.

RESULTS

Average annual excess costs for persistent patients were $4412 for health care and $924 for workloss (P < 0.01). Although costs for severe patients were higher than moderate patients (P < 0.05), moderate patients' costs were similar to that for mild patients. Persistent use of inhaled corticosteroids was lower in mild (9.0%) relative to moderate (78.1%) and severe (86.4%) patients.

CONCLUSIONS

Persistent asthma is expensive. Underutilization of inhaled corticosteroids is higher in patients with mild persistent asthma.

Distance between the skin and the thoracic paravertebral space

A fundamental requirement for the safe and effective performance of paravertebral blockade is reliable estimates of the depth from skin to paravertebral space at different thoracic levels. This distance was assessed using a nerve stimulator guided paravertebral blockade technique in 527 separate blocks in 186 patients scheduled for various surgical procedures on the trunk. The median skin-paravertebral depth was 55.0 mm. The skin-paravertebral distance at upper (T1-3) and lower (T9-12) thoracic levels were significantly greater than mid-thoracic levels (T4-8) (p < 0.05). Body mass index significantly influences this depth at upper and lower thoracic levels (p < 0.001) but not in the mid-thoracic region.

Consensus conference. Colorectal cancer: prevention, screening and management

We report in this section a series of consensus conferences organized and published by official and well known organizations. They are of general and public interest and can be used as clinical guidelines. We will be ready to report any consensus conference organized methodologically in Lebanon by medical societies or other scientific organizations.

[Diagnosis and treatment of hydatid cysts of the liver. Apropos of 87 cases operated on between 1980 and 1992]

Human echinococcosis is still endemic in some areas of the world, including Mediterranean countries and Lebanon. Because there is no effective medical therapy, surgery remains the principal mode of treatment. A consecutive series of 87 patients operated on for liver hydatid disease between January 1980 and March 1992 in the division of General Surgery at Saint George's Hospital, Beirut, were analyzed. Patients with hydatic cysts in other sites than liver were excluded from the study. There were 39 men (45%), and 48 women (55%) aged 12 to 75 years (mean 43). The right lobe of the liver was affected in 67 cases (77%), the left lobe in 18 cases (20.6%), and both lobes in 2 cases (2.4%). Clinical symptomatology consisted of abdominal pain, fever, jaundice, urticaria, and an abdominal mass. Preoperative diagnosis was established using imaging studies: plain abdominal films, ultrasonography, computed tomography, and serologic tests. Cases were classified into 3 groups: G1 (n = 44, 50.5%) had a partial resection of the cyst followed by an external drainage; G2 (n = 15, 17.2%) had a partial resection of the cyst with a filling of the residual cavity; G3 (n = 28, 32.2%) made benefit of complete resection of the cyst (pericystectomy) with or without partial hepatectomy. In this retrospective study we compared the results of these different surgical techniques: postoperative complications and mortality, hospital stay of patient. We noted the better postoperative course of the non-drained patient (G2 and G3). Three patients died during the postoperative period because of septic complications. Conclusions and general recommendations are proposed.

[Infection caused by Mycobacterium tuberculosis with primary resistance to multiple drugs: a case report of a patient with AIDS]

Primary multidrug-resistant Mycobacterium tuberculosis is an important problem in the United States. There is no report in formal literature of this pathogen in Brazilian patients. CASE REPORT--We report a case of ganglionar tuberculosis diagnosed by acid-fast smears in a male, HIV positive patient. Mode of acquisition of HIV was not determined. Treatment was started, and isoniazid, rifampicin and pyrazinamide were prescribed. The patient and his family reported strict adherence to therapy, but no improvement was observed. After 75 days, the patient was admitted in our hospital because of clinical worsening. Clinical features were the presence of large submandibular and axillar lymph nodes, respiratory insufficiency and complains of abdominal pain. He died six days after admission. Culture obtained from the ganglionar aspirate disclosed M. tuberculosis susceptible to ethambutol, but resistant to isoniazid, rifampicin, pyrazinamide, ethionamide and streptomycin. DISCUSSION--Although this was a case of extrapulmonary tuberculosis, there is a concern about multidrug-resistant tuberculosis, that has been poorly evaluated in Brazil. Since high lethality and intrahospital transmission have been reported, we discuss the need of performing culture and antibiogram in suspected cases, and the prevention of the spread of M. tuberculosis to patients and health-care workers through the strict adherence to the isolation practices.

[Silicone implants and breast cancer: real or fictitious problem? A case report and review of the literature]

We present a case of breast cancer 9 years after subcutaneous mastectomy for bilateral phylloid tumor with silicone implants. The patient had a stage III adenocarcinoma (T4 N1 M0) at diagnosis; a modified radical mastectomy was done, followed by radiotherapy and chemotherapy. Later on, Tamoxifen was prescribed (positive hormone receptors). Reviewing the literature about this subject in a context of a moratorium of the Food and Drug Administration (FDA) in the United States recommending suspension of silicone breast implantation, we can propose several conclusions: Previous and recent studies did not show any direct relation between cancer and silicone implants for augmentation mammoplasty; on the contrary, a lower incidence of breast cancer is noted. Breast cancer incidence with silicone implants seems to be higher with reconstructive mammoplasty after mastectomy for benign disease (fibrocystic disease, dysplasia, phylloid tumor), or prophylactic reason, or malignancy (carcinoma in situ, lobular and multifocal carcinoma, early breast cancer...). This can be related to recurrence or cancer development on residual breast tissue. Breast cancer with silicone implants is of poorer prognosis because of the later diagnosis of the disease.

Chloride transport across rat ileal basolateral membrane vesicles

The present study was designed to investigate Cl- transport across rat ileal basolateral membranes. Basolateral membrane vesicles were prepared by a well-validated technique. The purity of the basolateral membrane vesicles was verified by marker enzyme studies and by studies of d-glucose and calcium uptake. Cl- uptake was studied by a rapid filtration technique. Neither an outwardly directed pH gradient, nor a HCO3- gradient, or their combination could elicit any stimulation of Cl- transport when compared with no gradient. 4,4-Diisothiocyanostilbene-2,2-disulfonic acid at 5 mM concentration did not inhibit Cl- uptake under gradient condition. Similarly, the presence of the combination of outwardly directed Na+ and HCO3- gradients did not stimulate Cl- uptake compared with the combination of K+ and HCO3- gradients or no HCO3- gradient. This is in contrast to our results in the brush border membranes, where an outwardly directed pH gradient caused an increase in Cl- uptake. Cl- uptake was stimulated in the presence of combined Na+ and K+ gradient. Bumetanide at 0.1 mM concentration inhibited the initial rate of Cl- uptake in the presence of combined Na+ and K+ gradients. Kinetic studies of bumetanide-sensitive Cl- uptake showed a Vmax of 5.6 +/- 0.7 nmol/mg protein/5 sec and a Km of 30 +/- 8.7 mM. Cl- uptake was stimulated by an inside positive membrane potential induced by the ionophore valinomycin in the setting of inwardly directed K+ gradient compared with voltage clamp condition. These studies demonstrate two processes for Cl- transport across the rat ileal basolateral membrane: one is driven by an electrogenic diffusive process and the second is a bumetanide-sensitive Na+/K+/2 Cl- process. Cl- uptake is not enhanced by pH gradient, HCO3- gradient, their combination, or outwardly directed HCO3- and Na+ gradients.

Ontogeny of the Na(+)-H+ exchanger in rat ileal basolateral membrane vesicles

This study was designed to examine the activity of the Na(+)-H+ exchanger across the basolateral membranes of the ileal enterocyte and its developmental pattern. The function of the Na(+)-H+ exchanger was studied using a well validated basolateral membrane vesicle technique. Na+ uptake represented transport into the vesicle rather than binding as validated by initial rate studies. Na+ uptake represented an electroneutral process as shown by studies in which negative membrane potential was induced by the ionophore valinomycin. Various outwardly directed pH gradients significantly stimulated Na+ uptake compared with no pH gradient conditions at all age groups. However, the magnitude of stimulation was significantly different between the age groups with more marked stimulation of amiloride-sensitive Na+ uptake occurring in adolescent rats as compared to weanling or suckling rats. The amiloride sensitivity of the pH stimulated Na+ uptake was investigated using [Amiloride] = 10(-2)-10(-5) M at pHi/pHo = 5.2/7.5. At 10(-2) M amiloride concentration, Na+ uptake was inhibited by 80%, 70%, 77%, in the basolateral membranes of adolescent, weanling and suckling rats, respectively. Dixon plot analysis in both adolescent and weanling rats was consistent with two amiloride binding sites, a low affinity system and a high affinity system. In the suckling rat, on the other hand, the data supported a single high affinity binding site. Kinetic studies revealed a Km for amiloride-sensitive Na+ uptake of 12.6 +/- 6.6, 10.2 +/- 1.77, 9.46 and Vmax of 4.83 +/- 1.22, 4.47 +/- 0.36 and 8.08 +/- 1.92 n.mol.mg.protein-1.7 s-1 in suckling, weanling and adolescent rats, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)