Global parental leave in surgical careers: differences according to gender, geographical regions and surgical career stages

BACKGROUND

There is a lack of information regarding the provision of parental leave for surgical careers. This survey study aims to evaluate the experience of maternity/paternity leave and views on work-life balance globally.

METHODS

A 55-item online survey in 24 languages was distributed via social media as per CHERRIES guideline from February to March 2020. It explored parental leave entitlements, attitude towards leave taking, financial impact, time spent with children and compatibility of parenthood with surgical career.

RESULTS

Of the 1393 (male : female, 514 : 829) respondents from 65 countries, there were 479 medical students, 349 surgical trainees and 513 consultants. Consultants had less than the recommended duration of maternity leave (43.8 versus 29.1 per cent), no paid maternity (8.3 versus 3.2 per cent) or paternity leave (19.3 versus 11.0 per cent) compared with trainees. Females were less likely to have children than males (36.8 versus 45.6 per cent, P = 0.010) and were more often told surgery is incompatible with parenthood (80.2 versus 59.5 per cent, P < 0.001). Males spent less than 20 per cent of their salary on childcare and fewer than 30 hours/week with their children. More than half (59.2 per cent) of medical students did not believe a surgical career allowed work-life balance.

CONCLUSION

Surgeons across the globe had inadequate parental leave. Significant gender disparity was seen in multiple aspects.

Complications and functional outcomes after ileo-anal pouch excision-a systematic review of 14 retrospective observational studies

PURPOSE

The ileo-anal pouch (IAP) has been the gold standard procedure for maintenance of bowel continuity after panproctocolectomy for ulcerative colitis, familial adenomatous polyposis or hereditary non-polyposis colorectal cancer. However, the IAP has an estimated failure rate of 13% at 10 years post-procedure (Tulchinsky et al., Ann Surg 238(2):229-34, 2003), which can result in pouch excision (P.E.). This systematic review aims to synthesise all the available studies reporting post-operative outcomes of P.E. and its impact on patient quality of life (QoL), when available, which have not previously been summarised.

METHODS

PubMed, Embase, Medline and the Cochrane library databases were searched with terms 'Pouch AND excision' OR 'Pouch AND removal' OR 'Pouch AND remove' OR 'IAP AND excision'. All studies reporting post-operative morbidity, mortality or functional outcomes in patients who had P.E. were included. Studies with < 5 patients, non-English studies and conference abstracts were excluded.

RESULTS

14 studies comprising 1601 patients were included. Overall complications varied from 18 to 63% with the most common being persistent perineal sinus (9-40%) or surgical site infection (wound-2 to 30%; intra-abdominal collection-3 to 24%). The mortality rate was between 0.58 and 1.4%. QoL is generally lower in P.E. patients compared to the normal population across various QoL measures and P.E. patients often had urinary and sexual dysfunction post-operatively.

CONCLUSIONS

There is a substantial incidence of complications after P.E.; however, there is no evidence describing QoL pre- and post-P.E. Further longitudinal research comparing QoL in patients undergoing P.E. and other treatment options such as indefinite diversion is required to definitively assess QoL post-procedure.

Treatment of pediatric pyogenic granuloma in a functionally and cosmetically sensitive area with the 1064nm ND:Yag laser

There has been increasing interest in minimally invasive approaches to treat pyogenic granulomas. We report successful treatment of a pyogenic granuloma in a pediatric patient on a functionally and cosmetically sensitive area using the 1064nm Nd:YAG laser.

IgM ocular cicatricial pemphigoid: a unique insight into the immune system

A 42-year-old man with ocular erythema and scarring had a conjunctival biopsy revealing depostion of IgM and C3 without IgG at the epithelial basement membrane zone.  Treatment with doxycyline, dapsone, and mycophenolate mofetil was unsuccessful and treatment with rituximab has led to partial remission of the conjunctival inflammation. He has undergone 4 cycles of rituximab treatment at intervals of 12 to 18 months.

Paradoxical Induction of Psoriasis and Lichen Planus by Tumor Necrosis Factor-α Inhibitors

Case 1. A 33-year-old white woman presented to our clinic with a new-onset psoriasiform pustular eruption involving her palms and soles 4 months after the initiation of adalimumab for Crohn's disease. Her medical history was significant for childhood atopic dermatitis and hidradenitis suppurativa, but she had no personal or family history of psoriasis. Topical corticosteroids including hydrocortisone 2.5%, triamcinolone 0.1%, fluocinonide 0.05%, and clobetasol 0.05% were used without improvement. The pustular eruption spread to her scalp, trunk, and proximal extremities, and her toenails developed onycholysis and dystrophy. Her adalimumab was withdrawn for 1 month due to suspicion of a paradoxical pustular psoriasis reaction. After 2 weeks off adalimumab, the pustular dermatosis had significantly diminished and her gastroenterologist changed her medication to methotrexate. Her eruption continued to clear over the course of the next 6 months.

HSV-2 meningoencephalitis in an immunocompetent young man: what is the pathogenesis and what is the treatment?

Herpes simplex encephalitis is rarely caused by herpes simplex virus type 2 (HSV-2) after the neonatal period. The pathogenesis of HSV-2 encephalitis is not known and its treatment has not been discussed. We report a case of mild meningoencephalitis secondary to HSV-2 primary infection after sexual risk behaviour in a healthy young man. The diagnosis was established upon clinical, biological and electroencephalographic criteria. Aciclovir treatment led to rapid clinical improvement. This case highlights HSV-2 as a rare cause of meningoencephalitis, and questions the management of this rare manifestation of HSV-2 infection.

Adalimumab Induced Subcutaneous Nodular Sarcoidosis; A Rare Side Effect of Tumor Necrosis Factor-α Inhibitor

Adalimumab and other tumor necrosis factor-α inhibitors have been shown in the recent years to successfully treat sarcoidosis refractory to systemic corticosteroids and other agents.  However, there have been an increasing number of cases of sarcoidosis paradoxically induced by these agents.  It is hypothesized that this is due to the disruption of the fine balance of cytokines involved in granuloma formation. We describe the first case of adalimumab-induced subcutaneous nodular sarcoidosis in a patient with pulmonary sarcoidosis.

Hair-thread tourniquet syndrome: a case report and review of treatment

Hair-thread tourniquet syndrome (HTTS) is caused by circumferential constriction of an appendage, usually by hair or thread, leading to obstruction of circulation and ischemia. Although not rare, this entity is not discussed extensively in the Dermatology literature. We present a case of HTTS and discuss the demographics and etiology, and review the most current treatment methods.

Successful long-term thalidomide therapy for discoid lupus erythematosus-lichen planus overlap syndrome

Although thalidomide is a U.S. Food and Drug Admistration (FDA) approved medication for erythema nodosum leprosum and multiple myeloma, it has many off-label uses, including for discoid lupus erythematosus (DLE), Behçet's disease, apththous ulcers in HIV patients, and prurigo nodularis. Herein, we present a patient with an overlap of discoid lupus erythematosus and lichen planus who was successfully treated with thalidomide for over 19 years without significant side effects. We propose that some of the most common side effects, including peripheral neuropathy, numbness, parasthesias, sedation, and constipation, can be avoided at lower doses, typically less than 100mg/day.

The association between postprandial urinary C-peptide creatinine ratio and the treatment response to liraglutide: a multi-centre observational study

AIMS

The response to glucagon-like peptide 1 receptor agonist treatment may be influenced by endogenous β-cell function. We investigated whether urinary C-peptide creatinine ratio assessed before or during liraglutide treatment was associated with treatment response.

METHODS

A single, outpatient urine sample for urinary C-peptide creatinine ratio was collected 2 h after the largest meal of the day among two separate groups: (1) subjects initiating liraglutide (0.6 → 1.2 mg daily) or (2) subjects already treated with liraglutide for 20-32 weeks. The associations between pretreatment and on-treatment urinary C-peptide creatinine ratio and HbA1c change at 32 weeks were assessed using univariate and multivariate analyses (the ratio was logarithm transformed for multivariate analyses). Changes in HbA1c according to pretreatment urinary C-peptide creatinine ratio quartiles are shown.

RESULTS

One hundred and sixteen subjects (70 pretreatment, 46 on treatment) with Type 2 diabetes from 10 diabetes centres were studied. In univariate analyses, neither pretreatment nor on-treatment urinary C-peptide creatinine ratio correlated with HbA1c change (Spearman rank correlation coefficient, r = -0.17, P = 0.17 and r = -0.20, P = 0.19, respectively). In multi-linear regression analyses, entering baseline HbA1c and log urinary C-peptide creatinine ratio, pretreatment and on-treatment log urinary C-peptide creatinine ratio became significantly associated with HbA1c change (P = 0.048 and P = 0.040, respectively). Mean (sd) HbA1c changes from baseline in quartiles 1 to 4 of pretreatment urinary C-peptide creatinine ratio were -3 ± 17 mmol/mol (-0.3 ± 1.6%) (P = 0.52), -12 ± 15 mmol/mol (-1.1 ± 1.4%) (P = 0.003), -11 ± 13 mmol/mol (-1.0 ± 1.2%) (P = 0.002) and -12±17 mmol/mol (-1.1±1.6%) (P=0.016), respectively.

CONCLUSIONS

Postprandial urinary C-peptide creatinine ratios before and during liraglutide treatment were weakly associated with the glycaemic response to treatment. Low pretreatment urinary C-peptide creatinine ratio may be more useful than higher values by predicting poorer glycaemic response.

Using acupuncture to treat depression: a feasibility study

OBJECTIVES

To establish the feasibility of conducting a randomised controlled trial to evaluate the efficacy of acupuncture in the treatment of mild-to-moderate depression. Control group intervention, blinding of treatment, outcome measures and the acceptability of such a trial amongst participants were key factors to be addressed. The findings from this study will be used to determine the design of a phase III randomised controlled trial.

DESIGN

Nineteen participants were recruited through general practices in London, UK. Participants were randomly assigned on a 2:1 basis to either 12 sessions of verum acupuncture or 12 sessions of sham acupuncture (control). Sham acupuncture involved actual needling but at sites considered to be unrelated to depression.

MAIN OUTCOME MEASURES

The Beck's Depression Inventory (BDI) and the RAND 36 Item Health Survey 1.0 (RAND) were completed at baseline and at the end of treatment or at treatment dropout. All participants also attended a brief qualitative interview at the end of the study.

RESULTS

Treatment dropout was low and there were high levels of patient enthusiasm for a study of acupuncture. Referrals from General Practitioners (GPs) were lower than expected. The sham control method successfully maintained participant blinding to treatment and enabled the specific (or active) component of an acupuncture intervention to be isolated and its efficacy assessed. The outcome measures were sensitive enough to record changes in depressive symptoms and quality of life and are appropriate for use in a larger trial.

CONCLUSIONS

This feasibility study has provided important information that can be used to guide the design and methodology of a full-randomised controlled trial.

Practical management strategies for diaper dermatitis

Common diaper dermatitis is an irritant contact diaper dermatitis (IDD) created by the combined influence of moisture, warmth, urine, feces, friction, and secondary infection. It is difficult to completely eradicate these predisposing factors in a diapered child. Thus, IDD presents an ongoing therapeutic challenge for parents, family physicians, pediatricians, and dermatologists. This article will focus on practical management strategies for IDD.

Characterization of nelfinavir binding to plasma proteins and the lack of drug displacement interactions

OBJECTIVES

To determine the characteristics of the binding of nelfinavir and active M8 to alpha1-acid glycoprotein (AAG) and human serum albumin (HSA), and to examine the displacement effects of drugs binding extensively to AAG (ritonavir and saquinavir) or to HSA (salicylic acid and valproic acid).

METHODS

Free drugs were separated by equilibrium dialysis after incubation with human plasma or purified plasma proteins and after co-incubation with potential displacers. Association constants were estimated from double-reciprocal plots of the data.

RESULTS

Nelfinavir and M8 free fractions [fractions of unbound drug (fus)] were 0.42+/-0.08% (mean+/-standard deviation) and 0.64+/-0.07%, respectively. For the two analytes, respectively, association constants were 7.25 x 10(7)/m and 3.33 x 10(7)/m for AAG and 1.11 x 10(6)/m and 7.92 x 10(5)/m for HSA. Nelfinavir fu in an AAG solution was significantly (P < 0.01) increased by the addition of ritonavir or saquinavir, whereas it was unaltered by addition of these drugs to whole plasma. Similarly, fu in an HSA solution was significantly increased (P < 0.01) by the addition of salicylic acid or valproic acid, whereas there was no difference in the free fraction in plasma.

CONCLUSIONS

The affinity of nelfinavir for human plasma proteins was higher than that of M8, and both nelfinavir and M8 showed higher affinity to AAG than to HSA. The free fraction of nelfinavir was not affected by drugs that bind extensively to AAG or albumin when these drugs were added to whole plasma in combination, suggesting a compensatory effect of alternate binding proteins.

Meal-dependent regulation of circulating glycated insulin in type 2 diabetic subjects

There is mounting evidence that elevated circulating concentrations of glycated insulin play a role in insulin resistance in type 2 diabetes. This study evaluated the secretion of glycated insulin in response to enteral stimulation in type 2 diabetic subjects. Following a mixed meal (450 kcal; 44 % carbohydrate; 40 % fat; 16 % protein), glycated insulin rose 10-fold to peak (60 min) at 104.5 +/- 25.0 pmol/l (p < 0.001), representing 22 % total circulating insulin. The response paralleled early rises in insulin and C-peptide, which peaked at 90 min and were more protracted. Maximum glucose concentrations were observed at 50 min. These data indicate that type 2 diabetic subjects exhibit a rapid meal-induced release of glycated insulin from readily releasable pancreatic beta-cell stores, which might contribute to impaired glucose homeostasis following enteral nutrition.

The effect of manipulation of basal pulsatile insulin on insulin action in Type 2 diabetes

AIM

Disordered insulin pulsatility is associated with insulin resistant states including Type 2 diabetes. However, whether abnormal basal insulin pulses play a role in the pathogenesis of insulin resistance or are simply an associated feature remains undetermined. We investigated this relationship further by studying the effect of overnight (10 h) pulsatile insulin infusion on subsequent insulin sensitivity.

METHODS

We studied 17 Type 2 diabetic patients who underwent one of two protocols. In protocol A (10 patients) on two separate nights we infused insulin 0.1 mU/kg/min either in a constant infusion or in pulses every 13 min. Octreotide (0.43 microg/kg/h) was given to suppress endogenous insulin secretion and physiological replacement of glucagon (30 ng/kg/h) administered. Insulin sensitivity was measured using a hyperinsulinaemic euglycaemic clamp (2 mU/kg/min) next morning. In protocol B (seven patients), we employed the same experimental procedure but used a basal insulin infusion rate of 0.09 mU/kg/min in 7-min or 13-min pulses.

RESULTS

Appropriate pulse patterns were confirmed in each protocol. In protocol A, after overnight infusions, glucose infusion rates required to maintain euglycaemia at steady state hyperinsulinaemia were similar (33.9 +/- 5.2 vs. 31.2 +/- 4.1 micromol/kg/min; P = NS). In protocol B, after overnight infusions the glucose infusion rates required during hyperinsulinaemia were significantly lower during 7-min pulses (39.9 +/- 5.7 vs. 44.7 +/- 5.6 micromol/kg/min; P < 0.05).

CONCLUSION

There was no demonstrable priming effect derived from overnight pulsatile insulin compared with constant insulin infusion on subsequent insulin sensitivity in Type 2 diabetic subjects. The failure of 7-min pulses to exhibit an advantageous effect over 13-min pulses raises questions about the natural frequency of basal insulin pulses and their biological effect.

Integrating Western medicine and Traditional Chinese medicine in GP surgeries and the community: a review of the two pilot schemes

The popularity of complementary medicine has been relentless over the past decade. Among the most popular are Traditional Chinese Medicine (TCM) which has a long and unbroken history. This article reports on two integrated health care pilot schemes where TCM and Western medicine are merged, to varying degrees, for the benefits of patients. One of the schemes focuses on general medicine whilst the other focuses on mental health. The authors conclude that the integrated schemes have many advantages and, on the whole, are beneficial for patients. The issues involved and learning points are discussed.

Infectious mononucleosis in an outpatient population: diagnostic utility of 2 automated hematology analyzers and the sensitivity and specificity of Hoagland's criteria in heterophile-positive patients

OBJECTIVES

To determine the sensitivity and specificity of 2 modern hematology analyzers in flagging heterophile-positive patients; to determine if heterophile-positive, instrument-flagged specimens contain a larger number or a different spectrum of atypical lymphocytes; to document the overall sensitivity and specificity of Hoagland's morphologic criteria in identifying heterophile-positive patients in an outpatient population with a clinical diagnosis of mononucleosis; and to examine whether individual morphologic features might aid in the diagnosis of suspected infectious mononucleosis.

DESIGN

A prospective study of patients referred with a clinical diagnosis of infectious mononucleosis who subsequently tested positive for the heterophile antibody. The control group consisted of a similar population of patients who tested negative for the heterophile antibody.

INTERVENTION

Hematology profiles of peripheral blood samples were determined with Coulter STKS and Sysmex NE-8000 analyzers. A corresponding Wright-Giemsa-stained blood smear was subsequently examined by a single skilled technologist, who performed a 200-cell white blood cell differential and a 200-cell lymphocyte differential. A specific morphologic search was made for the presence of smudge cells or lymphocytes with cloverleaf nuclei.

RESULTS

Using a combination of all flagging criteria, the 2 analyzers identified 156 (86.2%) of 181 heterophile-positive patients as meriting further review. The sensitivity and specificity values of the Coulter analyzer in predicting positive heterophile status for the blast flag were 41% and 97.1%, respectively; for the variant lymphocyte flags, 72.4% and 79.1%, respectively; and for both flags, 40% and 98.1%, respectively. For the Sysmex analyzer, the sensitivity and specificity values in predicting positive heterophile status for the blast flag were 43.4% and 88.6%, respectively; for the variant lymphocyte flag, 15.8% and 90.8%, respectively; and for both flags, 10.5% and 96%, respectively. Considering the classic criteria developed by Hoagland, a lymphocytosis of at least 50% was present in 120 (66.3%) heterophile-positive patients, while an atypical lymphocytosis of at least 10% of the total WBC count was noted in 135 patients (74.6%). The sensitivity and specificity values of a lymphocytosis > or =50% for diagnosing heterophile-positive status were 66.3% and 84.5%, respectively, while the sensitivity and specificity of an atypical lymphocytosis > or =10% were 74.6% and 92.3%, respectively. The presence of smudge cells or cloverleaf lymphocyte nuclei was verified as having high specificity but low sensitivity for suggesting a diagnosis of infectious mononucleosis.

CONCLUSION

Although a number of patients did not meet Hoagland's criteria for the diagnosis of infectious mononucleosis, the flagging systems of modern hematology analyzers successfully identified most cases as requiring further review.

Effect of food on the bioavailability of SDZ DJN 608, an oral hypoglycemic agent, from a tablet and a liquid-filled capsule in the dog

PURPOSE

The effect on food on the bioavailability of SDZ DJN 608, a D-phenylalanine derivative, was investigated in three mature, male beagle dogs.

METHODS

Each dog received, under fasting and postprandial conditions, a 30 mg oral dose as a tablet (T) and a liquid-filled capsule (LC). Additionally, a 5 mg intravenous dose was given in the fasting state. Doses in the same dog were separated by 1-week washout periods. Serial plasma samples were collected for 24 h postdose and analyzed for SDZ DJN 608 using HPLC. Model-independent pharmacokinetic parameters were compared between treatments by 3-way ANOVA: In vitro dissolution profiles of T and LC were generated using the USP paddle method. In addition, the transport of SDZ DJN 608 through a Caco-2 cell monolayer was examined at concentrations of 0.1 and 1 mM, in the absence and presence of an aromatic amino acid, L-alpha-methyldopa, the transport of which is mediated by the large neutral amino acid (LNAA) carrier.

RESULTS

In the dog, SDZ DJN 608 was rapidly absorbed. The peak plasma concentration (Cmax) averaged higher, and the peak time (tmax) shorter, after LC than T, though the differences were not statistically significant. This finding is consistent with in vitro dissolution data showing that, at both pH 1.2 and pH 6.8, the dissolution rate of LC was faster than that of T. No significant difference in the area under curve (AUC) was observed between LC and T, the absolute bioavailability of both being complete in the fasting state. Whereas the presence of food showed little effect on the tmax and Cmax of either dosage form, it significantly reduced the AUC, the effect (ca -20%) being not different between LC and T. In the Caco-2 model, the mucosal-to-serosal permeability of SDZ DJN 608 was independent of concentration and unaffected by L-alpha-methyldopa, suggesting passive diffusion of the former.

CONCLUSIONS

Food had little effect on the absorption rate but significantly reduced the bioavailability of SDZ DJN 608 regardless of the dosage form. This effect is unlikely to be caused by inhibition of the transepithelial transport of SDZ DJN 608 by amino acids in the diet.

beta-Lactamase of Lysobacter enzymogenes: cloning, characterization and expression of the gene and comparison of the enzyme to other lactamases

The gene for the periplasmic beta-lactamase of Lysobacter enzymogenes was isolated as part of a 1017 bp EcoRI fragment and the nucleotide sequence of the gene was determined. It has a G+C content of 71.5% and encodes a 27 amino acid signal sequence and the mature beta-lactamase of 276 amino acids which has a mass of 29,146 Da. The enzyme appears to be unique to L. enzymogenes but its amino acid sequence shows a high degree of homology with the amino acid sequences of the lactamase from Citrobacter diversus and other Class A beta-lactamases. The beta-lactamase gene of L. enzymogenes was expressed in Escherichia coli using pUC118 as the vector. The production of active beta-lactamase was highest after the active growth phase of the expression host and reached levels which were about three times higher than those obtained with L. enzymogenes.

Nucleotide sequence and characterization of the gene for secreted alkaline phosphatase from Lysobacter enzymogenes

Lysobacter enzymogenes produces an alkaline phosphatase which is secreted into the medium. The gene for the enzyme (phoA) was isolated from a recombinant lambda library. It was identified within a 4.4-kb EcoRI-BamH1 fragment, and its sequence was determined by the chain termination method. The structural gene consists of an open reading frame which encodes a 539-amino-acid protein with a 29-residue signal sequence, followed by a 119-residue propeptide, the 281-residue mature phosphatase, and a 110-residue carboxy-terminal domain. The roles of the propeptide and the carboxy-terminal peptide remain to be determined. A molecular weight of 30,000 was determined for the mature enzyme from sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The amino acid sequence was compared with sequences available in the current protein data base, and a region of the sequence was found to show considerable homology with sequences in mammalian type 5 iron-containing purple acid phosphatases.

Aminoglycoside antibiotics preferentially increase permeability in phosphoinositide-containing membranes: a study with carboxyfluorescein in liposomes

The rate of release from multilamellar liposomes of the fluorescent probe carboxyfluorescein was determined as a measure of membrane permeability. Liposomes of phosphatidylcholine and different anionic phospholipids were incubated with low (1 microM) and high (3 mM) concentrations of calcium in the absence or presence of aminoglycoside antibiotics. The leakage of carboxyfluorescein into the medium was not caused by liposomal fusion as no vesicle fusion was observed in experiments with terbium and dipicolinic acid-loaded liposomes. The basal rate of carboxyfluorescein release (in the absence or presence of 1 microM calcium) from all types of liposomes ranged from 0.1 to 0.3% of trapped carboxyfluorescein per hour. The presence of 3 mM calcium caused the greatest increase in the rate of carboxyfluorescein release (about 9-fold) in liposomes containing phosphatidylinositol 4,5-bisphosphate (PIP2) whereas liposomes containing the other anionic phospholipids (phosphatidylserine, phosphatidylinositol and phosphatidylinositol 4-phosphate) showed an approximate 5-fold increase. In the presence of 1 microM calcium, the aminoglycosides neomycin and gentamicin also increased the rate of carboxyfluorescein release, with PIP2-containing liposomes showing a 3-5-times greater response than the other liposomes, releasing up to 4.6% of trapped carboxyfluorescein per hour. This drug-induced release was dose-dependent and antagonized by calcium. In the presence of 3 mM calcium, 0.1 mM gentamicin or neomycin were ineffective while the drug at 1 mM affected carboxyfluorescein release from PIP2-liposomes only. The aminoglycoside antibiotics, neomycin, gentamicin, tobramycin, kanamycin, amikacin, netilmicin, as well as neamine and spectinomycin (all at 0.1 mM) showed a graded effect on the rate of carboxyfluorescein release from PIP2-containing vesicles in the presence of 0.1 mM calcium. The magnitude of the effect correlated well with the ototoxicity of the drugs previously determined directly in cochlear perfusions in the guinea pig. The study demonstrates that aminoglycoside antibiotics are capable of altering membrane permeabilities and that this effect is most pronounced if PIP2 is present in the bilayers. The excellent correlation between this membrane action and the in-situ toxicity of the drugs further establishes the specific role of PIP2 in the molecular mechanism of aminoglycoside-induced hearing loss. Moreover, it confirms the usefulness of such physicochemical models for the screening and prediction of aminoglycoside toxicity.

Membrane effects of aminoglycoside antibiotics measured in liposomes containing the fluorescent probe, 1-anilino-8-naphthalene sulfonate

The mechanism of membrane disturbance by aminoglycoside antibiotics was investigated in liposomes containing the fluorescent probe, 1-anilino-8-naphthalene sulfonate (ANS). Liposomes of PC and different anionic phospholipids (1:1 to 15:1 molar ratios) were challenged with aminoglycosides in the presence of low (1 microM) and high (3 mM) concentrations of calcium. Liposomes containing PIP2 showed the greatest drug-induced changes in ANS fluorescence in the presence of high and low concentrations of calcium and at all PC:PIP2 molar ratios tested. Liposomes containing other anionic phospholipids (PS, PI and PIP) were not reactive toward aminoglycosides in the presence of 3 mM calcium or when the ratio of PC to anionic lipid was increased to 10:1. The aminoglycoside-induced changes of ANS fluorescence were not due to any changes in the emission spectrum of ANS, nor to changes in quantum yield, nor to a change in the binding affinity of ANS. It is concluded that a specific aminoglycoside-PIP2 interaction results in phase separation of PC and PIP2 and thus increases the number of available ANS binding sites in PC:PIP2 liposomes.

Membrane perturbation by aminoglycosides as a simple screen of their toxicity

A simple test to assess the toxicity of aminoglycosides was designed based on the interaction of these drugs with phosphatidylinositol bisphosphate. The fluorescent probe 1-anilino-8-naphthalene sulfonate was incorporated into liposomes composed of L-alpha-phosphatidylcholine and phosphatidylinositol bisphosphate (4:1 molar ratio), and changes in fluorescence induced by the aminoglycosides were measured. The magnitude of these changes correlated well with the intrinsic ototoxicity of the drugs previously established in cochlear perfusions: neomycin greater than gentamicin approximately equal to tobramycin greater than amikacin approximately equal to kanamycin approximately equal to netilmicin greater than neamine approximately equal to spectinomycin. Correlations were not accurate when other phospholipids were substituted for phosphatidylinositol bisphosphate. An alternative in vitro test, measurement of the zeta potential of liposomes, ranked the drugs according to their electrostatic charge but not their toxicity. These results suggest that: a simple screen for aminoglycoside toxicity can be established and perturbation of membranes containing phosphatidylinositol bisphosphate is a key step in aminoglycoside ototoxicity.