Binding of an antimicrobial peptide to bacterial cells: Interaction with different species, strains and cellular components.

Antimicrobial peptides (AMPs) selectively kill bacteria by disrupting their cell membranes, and are promising compounds to fight drug-resistant microbes. Biophysical studies on model membranes have characterized AMP/membrane interactions and the mechanism of bilayer perturbation, showing that accumulation of cationic peptide molecules in the external leaflet leads to the formation of pores ("carpet" mechanism). However, similar quantitative studies on real cells are extremely limited. Here, we investigated the interaction of the dansylated PMAP23 peptide (DNS-PMAP23) with a Gram-positive bacterium, showing that 107 bound peptide molecules per cell are needed to kill it. This result is consistent with our previous finding for Gram-negative strains, where a similar high threshold for killing was determined, demonstrating the general relevance of the carpet model for real bacteria. However, in the case of the Gram-positive strain, this number of molecules even exceeds the total surface available on the bacterial membrane. The high affinity of DNS-PMAP23 for the anionic teichoic acids of the Gram-positive cell wall, but not for the lipopolysaccharides of Gram-negative bacteria, provides a rationale for this finding. To better define the role of anionic lipids in peptide/cell association, we studied DNS-PMAP23 interaction with E. coli mutant strains lacking phosphatidylglycerol and/or cardiolipin. Surprisingly, these strains showed a peptide affinity similar to that of the wild type. This finding was rationalized by observing that these bacteria have an increased content of other anionic lipids, thus maintaining the total membrane charge essentially constant. Finally, studies of DNS-PMAP23 association to dead bacteria showed an affinity an order of magnitude higher compared to that of live cells, suggesting strong peptide binding to intracellular components that become accessible after membrane perturbation. This effect could play a role in population resistance to AMP action, since dead bacteria could protect the surviving cells by sequestering significant amounts of peptide molecules. Overall, our data indicate that quantitative studies of peptide association to bacteria can lead to a better understanding of the mechanism of action of AMPs.

Botryoid rhabdomyosarcoma of the nasopharynx.

A case report of a Stage III botryoid rhabdomyosarcoma of the nasopharynx associated with a six-and-a-half-year survival is presented. Treatment consisted of surgery, radiotherapy (6,000 rads TCT) to the nasopharynx and maxillary sinuses bilaterally, and six cycles of polychemotherapy with Vincristine, Adriamycin, Cyclophosphamide and DTIC, without major loss of function or cosmetic deformity. The histology of the lesion is discussed with reference to recent classification and prognosis. The authors suggest that the histological type and prognosis of rhabdomyosarcoma of the nasopharynx in children may be better correlated in future studies.

Echocardiographic abnormalities in patients with transfusion-dependent anemia and secondary myocardial iron deposition.

The heart was evaluated by echocardiography in 56 patients at risk for myocardial iron deposition. Fifty-four had congenital anemia for which they required repeated transfusions, and two had primary hemochromatosis. The data, plotted according to one of three functions of the body surface area, were compared to values obtained in 105 normal subjects whose age spanned a similar range. Left ventricular wall thickness, transverse dimension and mass, as well as left atrial transverse dimension, were increased in the majority of patients with chronic iron overload despite the infrequent occurrence of cardiac enlargement on routine chest films (32 per cent) or electrocardiographic abnormality (16 per cent). Left ventricular ejection fraction was normal in all but four patients. These four patients died within a six month follow-up period suggesting that deterioration in systolic function is an indicator of poor prognosis. Our findings indicate that echocardiography provides a simple noninvasive means for assessing changes in cardiac structure and function that should prove useful in the serial evaluation of patients who are at risk for the development of myocardial iron deposition.

Chelation studies with 2,3-dihydroxybenzoic acid in patients with beta-thalassaemia major.

2-3-Dihydroxybenzoic acid was evaluated as a potentially useful, orally effective iron-chelating drug by performing iron balance studies in patients with beta-thalassaemia major. The administration of this substance at 25 mg/kg/d to five patients for 8 d caused an average increase in iron excretion of 4.5 mg/d. When the drug was administered at 25 mg/kg q.i.d. to eight patients for 21 d, iron excretion increased to 6.5 mg/d. Chelation was highly specific for iron with changes in magnesium and calcium excretion being insignificant. The drug was well tolerated with side effects limited to gastrointestinal complaints which ameliorated when the drug was taken with food. These studies provide a rationale for further evaluation of 2,3-dihydroxybenzoic acid in patients with iron overload.

Fractures in thalassemia.

Fractures occur frequently in patients with homozygous beta-thalassemia. A study was made of the fractures noted in a group of patients who were followed at the Thalassemia Clinic at The New York Hospital-Cornell Medical Center. Results indicate that these patients often sustain fractures which are multiple and which frequently heal with resultant deformities.

Hepatocellular carcinoma, transfusion-induced hemochromatosis and congenital hypoplastic anemia (Blackfan-Diamond syndrome).

A 25 year old patient with congenital hypoplastic anemia (Black-fan-Diamond syndrome) is described. This patient was hepatitis-antigen negative, had not received androgens and had a hepatoma develop in a transfusional hemochromatotic liver. Since androgens have been associated with hepatocellular carcinoma, the use of androgenic steroids for other than life-threatening symptoms in this disease should be avoided.

PIP: In this case report, the patient had been delivered by Caesarean section and weighed only 4 pounds at birth. The mother was O negative, the father A positive, and the infant A positive. Initial red cell count was 2.85 million/cu mm; white cell count, 19,200/cu mm; and hemoglobin 70% of normal. At 3 months of age hemoglobin was 10% of normal. Bone marrow examination revealed marked erythroid hyperplasia. A diagnosis of Blackfan-Diamond syndrome was made. He received blood transfusions every 2 or 3 weeks for the first 4 years of his life. During his lifetime he received 433 units of packed cells for the treatment of congenital hypoplastic anemia. Vitamin-B12, folic acid, and iron were given without benefit. At 8 years of age a spelectomy was done. 20 months after surgery he recovered from pneumonococcal meningitis without sequelae. Progressive signs of hemochromatosis developed and finally progressive signs of heart failure with edema. At 24 years of age severe epigastric pain developed. An open liver biopsy disclosed multiple liver nodules which proved to be hepatoma. Severe ascites followed the surgery. Pulmonary metastases of the liver tumor developed and heart failure. He died at age 25. This patient had received no androgen. He was consistently hepatitis antigen negative. He was prepubertal at the age of 25 and had almost no endogenous androgens. Alpha-fetoglobin was present. This test may be useful as a screening test for hepatoma.

Fatal pulmonary hypersensitivity reaction to HL-A incompatible blood transfusion:report of a case and review of the literature.

A girl with Thalassemia major reacted to a transfusion of packed red blood cells with increasing respiratory distress until death 12 1/2 hours later. Chills and fever were followed by dry cough, dyspnea, and pulmonary edema. The recipient had lymphocytotoxic antibodies specific for donor leukocyte antigens HL-A11 and possibly W14. At autopsy, the lungs showed pulmonary edema with extensive nonspecific acute alveolar injury. Similar cases in the literature are reviewed.