Retrospective Observational Real-World Outcome Study to Evaluate Safety Among Patients With Erectile Dysfunction (ED) With Co-Possession of Tadalafil and Anti-Hypertensive Medications (anti-HTN)

BACKGROUND

Erectile dysfunction (ED) is a common condition affecting male adults and may be associated with hypertension, diabetes, hyperlipidemia, and obesity. Phosphodiesterase type 5 (PDE5) inhibitors, such as tadalafil, are the first-line drug therapy for ED. Studies and the current prescribing information of these PDE5 inhibitors indicate they are mechanistic mild vasodilators and, as such, concomitant use of a PDE5 inhibitor with anti-hypertensive medication may lead to drops in blood pressure due to possible drug-drug interaction.

AIM

Evaluate risks of hypotensive/cardiovascular outcomes in a large cohort of patients with ED that have co-possession of prescriptions for tadalafil and hypertensive medications versus either medication/s alone.

METHODS

A cohort study conducted within an electronic health record database (Optum) representing hospitals across the US. Adult male patients prescribed tadalafil and/or anti-hypertensive medications from January 2012 to December 2017 were eligible. Possession periods were defined by the time patients likely had possession of medication, with propensity score-matched groups used for comparison.

OUTCOMES

Risk of hypotensive/cardiovascular outcomes were measured using diagnostic codes and NLP algorithms during possession periods of tadalafil + anti-hypertensive versus either medication/s alone.

RESULTS

In total there were 127,849 tadalafil + anti-hypertensive medication possession periods, 821,359 anti-hypertensive only medication possession periods, and 98,638 tadalafil only medication possession periods during the study; 126,120 were successfully matched. Adjusted-matched incidence rate ratios (IRRs) for the anti-hypertensive only possession periods compared with tadalafil + anti-hypertensive periods of diagnosed outcomes were all below 1. Two outcomes had a 95% confidence interval (CI) that did not include 1.0: ventricular arrhythmia (IRR 0.79; 95% CI 0.66, 0.94) and diagnosis of hypotension (IRR 0.79; 95% CI 0.71, 0.89).

CLINICAL IMPLICATIONS

Provides real world evidence that co-possession of tadalafil and anti-hypertensive medications does not increase risk of hypotensive/cardiovascular outcomes beyond that observed for patients in possession of anti-hypertensive medications only.

STRENGTHS AND LIMITATIONS

EHR data are valuable for the evaluation of real world outcomes, however, the data are retrospective and collected for clinical patient management rather than research. Prescription data represent the intent of the prescriber and not use by the patient. Residual bias cannot be ruled out, despite propensity score matching, due to unobserved patient characteristics and severity that are not fully reflected in the EHR database.

CONCLUSION

In the studied real world patients, this study did not demonstrate an increased risk of hypotensive or cardiovascular outcomes associated with co-possession of tadalafil and anti-hypertensive medications beyond that observed for patients in possession of anti-hypertensive medications only. Nunes AP, Seeger JD, Stewart A, et al., Retrospective Observational Real-World Outcome Study to Evaluate Safety Among Patients With Erectile Dysfunction (ED) With Co-Possession of Tadalafil and Anti-Hypertensive Medications (anti-HTN). J Sex Med 2022;19:74-82.

Cardiovascular Outcome Risks in Patients With Erectile Dysfunction Co-Prescribed a Phosphodiesterase Type 5 Inhibitor (PDE5i) and a Nitrate: A Retrospective Observational Study Using Electronic Health Record Data in the United States

BACKGROUND

Phosphodiesterase type 5 inhibitors (PDE5i) are first-line therapy for erectile dysfunction (ED). Approximately 1-4% of PDE5i recipients co-possess nitrates, despite this combination potentially producing clinically significant hypotension. Real-world data in these patients and insights into prescriber rationales for co-prescription are limited.

AIM

This study investigated whether PDE5i and nitrate co-possession is associated with increased rates of cardiovascular (CV) outcomes.

METHODS

Adult males with ED and PDE5i prescription and males with nitrate prescription were identified from a U.S. electronic health record database (2012-2016). Quantitative comparisons were made between patients with ED and co-possession (ED + PDE5i + nitrate), only nitrate possession (ED + nitrate and nitrate only [without ED]), and only PDE5i possession (ED + PDE5i).

OUTCOMES

We quantified incidence of CV outcomes in co-possession and comparator periods, calculating incidence rate ratios after propensity score matching. Prescriber rationales were derived by reviewing virtual patient records.

RESULTS

Over 168,000 patients had ≥1 PDE5i prescription (∼241,000 possession periods); >480,000 patients had ≥1 nitrate prescription (∼486,000 possession periods); and 3,167 patients had 3,668 co-possession periods. Non-significantly different or lower rates of CV outcomes were observed for co-possession periods vs ED + nitrate and nitrate only periods. Most CV outcome rates were non-significantly different between co-possession and ED + PDE5i periods (myocardial infarction, hospitalized unstable angina and fainting were higher with co-possession). From qualitative assessment of patient records with co-possession, 131 of 252 (52%) documented discussion with a physician regarding co-possession; 69 of 131 (53%) warned or instructed on safely managing these contraindicated medications.

CLINICAL IMPLICATIONS

Findings from this real-world study indicate that co-possession of nitrate and PDE5i prescriptions is not associated with increased rates of CV outcomes, relative to possession of nitrates alone. Physicians should and often do discuss the risks of using both medications together with their patients.

STRENGTHS & LIMITATIONS

Strengths of this study are the large size of the U.S. real-world patient cohort with data available for analysis, and our ability to utilize natural language processing to explore co-prescription rationales and patient-physician interactions. Limitations are the retrospective nature of the analysis and inability to establish whether recorded prescriptions were filled or the medication was consumed.

CONCLUSION

Co-exposure of PDE5i and nitrates should continue to be avoided; however, co-possession of PDE5i and nitrate prescriptions is not necessarily associated with increased CV risk. Co-possession can be successfully managed in suitable circumstances. Nunes AP, Seeger JD, Stewart A, et al. Cardiovascular Outcome Risks in Patients With Erectile Dysfunction Co-Prescribed a Phosphodiesterase Type 5 Inhibitor (PDE5i) and a Nitrate: A Retrospective Observational Study Using Electronic Health Record Data in the United States. J Sex Med 2021;18:1511-1523.

Safety of polyethylene glycol 3350 solution in chronic constipation: randomized, placebo-controlled trial

Purpose

To evaluate the safety and tolerability of aqueous solution concentrate (ASC) of polyethylene glycol (PEG) 3350 in patients with functional constipation.

Patients and methods

The patients who met Rome III diagnostic criteria for functional constipation were randomized in this multicenter, randomized, placebo-controlled, single-blind study to receive once daily dose of PEG 3350 (17 g) ASC or placebo solution for 14 days. The study comprised a screening period (visit 1), endoscopy procedure (visits 2 and 3), and followup telephone calls 30 days post-treatment. Safety end points included adverse events (AEs), clinical laboratory evaluations, vital signs, and others. The primary end points were the proportion of patients with abnormalities of the oral and esophageal mucosa, detected by visual and endoscopic examination of the oral cavity and esophagus, respectively, compared with placebo. A secondary objective was to compare the safety and tolerability of ASC by evaluating AEs or adverse drug reactions.

Results

A total of 65 patients were enrolled in this study, 31 were randomized to PEG 3350 ASC and 34 were randomized to placebo, of which 62 patients completed the study. No patients in either group showed abnormalities in inflammation of the oral mucosa during visit 2 (before treatment) or visit 3 (after treatment). Fewer abnormalities of the esophageal mucosa were observed in the PEG 3350 ASC group than in the placebo group on visit 3, with no significant difference in the proportion of abnormalities between the treatment groups. Overall, 40 treatment-emergent AEs were observed in 48.4% of patients treated with PEG 3350 ASC, and 41 treatment-emergent AEs were observed in 55.9% of patients treated with placebo – nonsignificant difference of −7.5% (95% CI: −21.3, 6.3) between treatment groups. No serious AEs or deaths were reported, and no patient discontinued because of an AE.

Conclusion

PEG 3350 ASC is safe and well tolerated in patients with functional constipation (NCT01885104).

A randomized, crossover pharmacodynamic study of immediate-release omeprazole/sodium bicarbonate and delayed-release lansoprazole in healthy adult volunteers

Proton pump inhibitors (PPIs) effectively block gastric acid secretion and are the treatment of choice for heartburn. PPIs differ, however, in onset of action and bioavailability. In this single-center, open-label, three-way crossover study, onset of action of immediate-release omeprazole 20 mg/sodium bicarbonate 1100 mg (IR-OME) and delayed-release (DR) lansoprazole 15 mg was evaluated in 63 healthy fasting adults. Subjects were randomized to once daily IR-OME, or DR-lansoprazole, or no treatment for 7 days. The primary efficacy endpoint was the earliest time where a statistically significant difference was observed between IR-OME and DR-lansoprazole in median intragastric pH scores for three consecutive 5-min intervals on day 7. Secondary endpoints compared effects of active treatments on days 1 and 7 (e.g., time to sustained inhibition, percentage of time with pH >4). A significant difference in median intragastric pH favoring IR-OME was observed on day 7 starting at the 10- to 15-min interval postdosing (P = 0.024) and sustaining through the 115- to 120-min interval (P = 0.017). On day 1, IR-OME achieved sustained inhibition of intragastric acidity significantly faster than DR-lansoprazole. IR-OME maintained pH >4 significantly longer than DR-lansoprazole over a 24-h period (P = 0.007) on day 7. Overall, results of this study demonstrate IR-OME is safe and well tolerated and that treatment with IR-OME results in significantly faster onset of action and better gastric acid suppression at steady state than DR-lansoprazole.

Polyethylene glycol 3350 in occasional constipation: A one-week, randomized, placebo-controlled, double-blind trial

AIM: To evaluate the efficacy and safety of polyethylene glycol (PEG) 3350 in subjects with self-reported occasional constipation.

METHODS: Eligible subjects ≥ 17 years of age were randomized to receive either placebo or PEG 3350 17 g once daily in this multicenter, double-blind trial. Evaluations were conducted before (baseline) and after a 7-d treatment period. The primary efficacy variable was the proportion of subjects reporting complete resolution of straining and hard or lumpy stools. Secondary efficacy variables assessed the severity of the subjects’ daily bowel movement (BM) symptoms, and preference of laxatives based on diary entries, visual analog scale scores, and questionnaires.

RESULTS: Of the 203 subjects enrolled in the study, 11 had major protocol violations. Complete resolution was noted by 36/98 (36.7%) subjects in the PEG 3350 group and 23/94 (24.5%) in the placebo group (P = 0.0595). The number of complete BMs without straining or lumpy stools was similar between both groups. Subjects receiving PEG 3350 experienced significant relief in straining and reduction in hardness of stools over a 7-d period (P < 0.0001). Subjects reported that PEG 3350 had a better effect on their daily lives, provided better control over a BM, better relief from constipation, cramping, and bloating, and was their preferred laxative. Adverse events (AEs) were balanced between the PEG 3350 and the placebo groups. No deaths, serious AEs, or discontinuations due to AEs were reported. This trial is registered at clinicaltrials.gov as NCT00770432.

CONCLUSION: Oral administration of 17 g PEG 3350 once daily for a week is effective, safe, and well tolerated in subjects with occasional constipation.

Phenylephrine hydrochloride modified-release tablets for nasal congestion: a randomized, placebo-controlled trial in allergic rhinitis patients

BACKGROUND

Over-the-counter phenylephrine hydrochloride (PEH) is used for relief of nasal congestion caused by allergic rhinitis; however, data to support its efficacy are lacking. The US Food and Drug Administration recommended clinical trials to evaluate the efficacy and safety of PEH in patients with this condition.

OBJECTIVE

To evaluate the efficacy and safety of PEH 30-mg modified-release (MR) tablets in patients with nasal congestion caused by allergic rhinitis in a multicenter, randomized, double-blinded, placebo-controlled, 2-arm, parallel-group study.

METHODS

Eligible adults at least 18 years old with documented hypersensitivity to fall pollen allergens were randomized to PEH-MR or placebo every 12 hours for 7 days from August 30 to October 12, 2011. The primary end point was mean change from baseline during the entire treatment period in daily reflective nasal congestion score. Secondary end points included changes in other symptom score assessments, time to maximal effect, duration of effect, and quality of life. Safety assessments included adverse events, serious adverse events, vital signs, physical examination, and electrocardiograms.

RESULTS

Of 575 patients, 288 received PEH-MR and 287 received placebo. No significant beneficial difference was detected between PEH-MR and placebo for the primary end point (PEH-MR, mean -0.394, SD 0.4880; placebo, mean -0.412, SD 0.5383; P = .2655). Likewise, no significant differences were observed for most secondary end points or quality of life. Overall, 89 of 575 patients (15.5%), equally distributed between the PEH-MR and placebo groups, experienced at least 1 treatment-emergency adverse event.

CONCLUSION

PEH-MR 30-mg tablets taken orally every 12 hours for 7 days is not more efficacious than placebo in relieving nasal congestion caused by allergic rhinitis.

TRIAL REGISTRATION

clinicaltrials.gov, identifier NCT01413958, protocol CL2011-06.

Oral Phenylephrine HCl for Nasal Congestion in Seasonal Allergic Rhinitis: A Randomized, Open-label, Placebo-controlled Study

BACKGROUND

Phenylephrine hydrochloride (PE HCl) is widely used for the treatment of nasal congestion, but efficacy at the 10-mg dose is not known for certain. The Food and Drug Administration has requested that sufficiently powered, multicenter, dose-ranging studies be conducted to assess the efficacy and safety of PE HCl.

OBJECTIVE

To evaluate subjective nasal congestion symptom relief and safety of 4 different doses of PE HCl immediate-release 10-mg tablets and placebo in adults with seasonal allergic rhinitis (SAR).

METHODS

This multicenter, phase 2, parallel, open-label trial randomized 539 adults with SAR (but otherwise healthy) to 7 days of treatment with either PE HCl 10-mg tablets at fixed doses of 10, 20, 30, or 40 mg or placebo. The primary efficacy end point was the mean change from baseline over the entire treatment period in daily reflective nasal congestion score. Other efficacy end points and safety were also evaluated.

RESULTS

None of the PE HCl treatment groups had a statistically significant change from baseline in instantaneous or reflective nasal congestion scores compared with the placebo group. PE HCl was well tolerated at doses of up to 30 mg. At least 1 treatment-emergent adverse event was experienced by 18.4% of the participants, the most common being headache (3.0%).

CONCLUSIONS

PE HCl, at doses of up to 40 mg every 4 hours, is not significantly better than placebo at relieving nasal congestion in adults with SAR. The phenylephrine section of the Food and Drug Administration monograph on over-the-counter cold, cough, allergy, bronchodilator, and antiasthmatic products should be revised accordingly.

DT-MRI denoising and neuronal fiber tracking

Diffusion tensor imaging can provide the fundamental information required for viewing structural connectivity. However, robust and accurate acquisition and processing algorithms are needed to accurately map the nerve connectivity. In this paper, we present a novel algorithm for extracting and visualizing the fiber tracts in the CNS, specifically in the brain. The automatic fiber tract mapping problem will be solved in two phases, namely a data smoothing phase and a fiber tract mapping phase. In the former, smoothing of the diffusion-weighted data (prior to tensor calculation) is achieved via a weighted TV-norm minimization, which strives to smooth while retaining all relevant detail. For the fiber tract mapping, a smooth 3D vector field indicating the dominant anisotropic direction at each spatial location is computed from the smoothed data. Neuronal fibers are then traced by calculating the integral curves of this vector field. Results are expressed using three modes of visualization: (1) Line integral convolution produces an oriented texture which shows fiber pathways in a planar slice of the data. (2) A streamtube map is generated to present a 3D view of fiber tracts. Additional information, such as degree of anisotropy, can be encoded in the tube radius, or by using color. (3) A particle system form of visualization is also presented. This mode of display allows for interactive exploration of fiber connectivity with no additional preprocessing.

Gabapentin for treatment of neuropathic pain in a 12-year-old girl

We report on a 12-year-old girl with postthoracotomy neuropathic pain. A variety of treatments for the pain were ineffective. The symptoms resolved following the institution of therapy with gabapentin.

Oral midazolam premedication and postoperative behaviour in children

We examined the effect of oral midazolam premedication on postoperative behaviour. Seventy children (ASA Physical Status 1 and 2; aged 1-10 yrs) were assigned randomly in a prospective, blinded fashion to receive either midazolam 0.5 mg.kg-1 (maximum 10 mg) or placebo. Behaviour assessments were made prior to medication, during induction of anaesthesia and 15 min following arrival to recovery room. The baseline behavioural evaluation scores were not significantly different. The children receiving midazolam cried significantly less during induction (P < or = 0.02). At one week follow-up, eight of 35 subjects receiving placebo had experienced adverse behaviour changes (nightmares, night terrors, food rejection, anxiety, negativism); 19 of 35 of the midazolam group experienced these changes (P < or = 0.02). At four week follow-up, most behaviour changes had resolved. Children given preoperative oral midazolam were less likely to cry and fight while being anaesthetized, and preoperative sedation was associated with increased incidence of adverse postoperative behaviour changes.

Preparing children for the operating room: psychological issues

Children respond psychologically to the prospect of surgery in a variable and age-dependent manner. This review summarizes the psychoanalytic, cognitive, behavioural and family system models of child development. It then reviews studies of hospitalization and anaesthesia in children. These studies suggest that younger children, children previously anaesthetized, and children who experience turbulent anaesthetic inductions are at particular risk for postoperative behavioural disturbances. Strategies of dealing with children and their parents during the perioperative period are discussed. Such strategies include: allowing a parent to be present during induction of anaesthesia, administering sedative premedication, creating a supportive environment, educating children and parents (verbal descriptions, tours, books, videos), and establishing rapport with children and their parents. Age-specific techniques of establishing rapport with children are discussed. If children are less anxious during the perioperative period, not only will they often exhibit less behavioural disturbances postoperatively, but they may face subsequent medical care more easily.

Acute lymphoid changes and ongoing immune activation in SIV infection

Two features of simian immunodeficiency virus (SIV) infection are emphasized: a transitory decrease in CD4 T cells in the first 2 weeks of infection followed by CD8 T-cell rise, and immune cell activation occurring by 4 weeks and persisting throughout the illness. The short-term changes included a fall in CD4 T cells by 2 weeks with partial recovery by 4 weeks and a CD8 rise that starts at 2 weeks. Subsequent characterization of CD4 T cells showed reduced expression of HLA-DR and CD25 (IL-2 receptor alpha chain) antigens later in SIV infection. Immune cell activation is evident in increased serum levels of neopterin and soluble CD8 antigen. Serum beta 2-microglobulin changes are less marked. Activation of CD8 T cells is reflected by increased percentages of cells expressing HLA-DR antigen. The B-cell numbers increased late in the course of SIV infection. Increased expression of the CD78 (Leu 21) activation phenotype was also seen in some monkeys. The immune activation changes (serum neopterin levels) induced by SIV infection in rhesus macaques appear to be associated with duration of illness, although the number of monkeys observed until death were too few for conclusive data. Thus, immune activation as well as T-cell deficiency may reflect significant immunopathogenic processes in SIV-induced disease.

Toxoplasma serology, parasitemia and antigenemia in patients at risk for toxoplasmic encephalitis

In order to further characterize the pathogenesis of Toxoplasma gondii infection in patients with AIDS and AIDS-related complex (ARC), a cohort of HIV- and Toxoplasma-infected individuals were identified and prospectively followed. Four hundred and 10 HIV-infected individuals followed in the San Francisco General Hospital AIDS Clinic were screened for antibodies to Toxoplasma between November 1986 and November 1988. Of the 67 (16%) individuals seropositive for Toxoplasma antibodies, 33 (49%) were followed monthly for a mean duration of 7.5 months. One hundred and 11 follow-up blood samples were obtained in order to determine Toxoplasma serology and the incidence of parasitemia. In general, Toxoplasma immunoglobulin (Ig) G antibodies remained stable over time. Detection of Toxoplasma antigenemia and parasitemia was uniformly negative, including those specimens obtained from two individuals within 45 days of their developing toxoplasmic encephalitis.

Nucleotide sequence of the small double-stranded RNA segment of bacteriophage phi 6: novel mechanism of natural translational control

The lipid-containing bacteriophage phi 6 has a genome composed of three segments of double-stranded RNA. We determined the nucleotide sequence of a cDNA copy of the smallest RNA segment. The coding sequences of the four proteins on this segment were identified. These sequences were clustered. Three of the genes had overlapping initiation-termination codons. All noncoding sequences were at the ends of the molecule. The genes of the small double-stranded RNA segment comprised two translational polarity groups. We propose that the translational coupling is the result of an inability of ribosomes to bind independently to two of the four genes. Translation of these genes occurred when ribosomes were delivered to them by translation of an upstream gene.

cDNA cloning of portions of the bacteriophage phi 6 genome

Phage phi 6 has a genome consisting of three pieces of double-stranded RNA. Single-stranded RNA was prepared from phi 6 nucleocapsids by in vitro transcription with the phage RNA polymerase. These transcripts were polyadenylated and used as templates for the preparation of cDNA copies. The resulting DNA was cloned into the PstI restriction nuclease site of plasmid pBR322. Insert-bearing plasmids were annealed to phi 6 RNA to assign the inserts to their proper segments. In this way we identified inserts corresponding to the large, medium, and small segments. Two large overlapping inserts of the small segment constitute the complete complement of the segment as determined by the sequence analysis of the DNA. In vitro coupled transcription and translation showed that the small segment inserts were able to direct the synthesis of the four known genes in the small segment. Two overlapping inserts in the medium segment constitute the entire segment and were shown to direct the in vitro synthesis of two of the three known proteins of the medium segment. Several inserts bearing about one-third the complement of the large segment were also isolated, and one of these directed the synthesis of a peptide that resembles protein P1. Restriction endonuclease maps were prepared for the inserts, and by in vitro synthesis it was possible to refine the genetic map of phi 6. A chimeric plasmid was constructed that combines plasmids pUC8 and RSF1010. Inserts placed on this plasmid were transformed to Pseudomonas phaseolicola, the natural host of phage phi 6. It was possible to refine further the genetic map by complementation of nonsense mutants of phi 6 with the cDNA.

Identification of a protein bound to the termini of bacteriophage PRD1 DNA

Lipid-containing bacteriophage PRD1 has a double-stranded DNA genome of about 14,500 nucleotide base pairs. The phage can infect Escherichia coli and Salmonella typhimurium as well as other gram-negative bacteria harboring an appropriate plasmid. [35S]methionine label is incorporated into the DNA band early in infection. The label remains associated with DNA through phenol extraction and boiling with sodium dodecyl sulfate. Nuclease treatment of the genome released a protein which migrated as an early phage-specific protein (P8). This protein is also necessary for phage DNA replication. By restriction enzyme analysis it was shown that protein was associated with the terminal restriction fragments. Extracts of infected cells catalyzed the labeling of protein P8 with [alpha-32P]dGTP.

Molecular cloning of bacteriophage PRD1 genomic fragments

DNA from bacteriophage PRD1 was extracted and partially digested with restriction endonuclease HaeII. The digest was cloned into the PstI site of plasmid pBR322 by homopolymer tailing with guanidylate tails on the plasmid and cytidylate tails on the phage DNA. Insert bearing plasmids were isolated by transforming E. coli strains for tetracycline resistance and screening for ampicillin sensitivity. These strains were then screened for the ability to accomplish marker rescue of nonsense mutants of bacteriophage PRD1. Additional clones were isolated by screening transformants with radioactively labeled probe PRD1 DNA fragments using colony hybridization. A genetic map was generated by the marker rescue capabilities of overlapping cloned inserts. This map allowed the ordering of fourteen of the known PRD1 complementation groups.

Establishment of a physical and genetic map for bacteriophage PRD1

DNA was isolated from the lipid-containing bacteriophage PRD1 and subjected to restriction endonuclease analysis. The total genome size is 14.7 kb. PRD1 DNA was resistant to cutting by fifteen restriction endonucleases with six base specificity. HaeII made thirty-seven cuts in the DNA, MboI made one cut, and MnlI made six cuts. DNA that was not treated with protease yielded two fewer fragments when treated with HaeII. Evidence is presented to indicate that the PRD1 DNA has protein at the ends of the DNA. The thirty-eight HaeII fragments were ordered using the ladder technique of Smith and Birnstiel (1976) on MboI and MnlI fragments of the genome. Clones of HaeII partial digests of PRD1 DNA in pBR322 were analyzed by HaeII digestion and were then assigned to specific regions of the genome by their HaeII fragment composition. A comparison of the marker rescue characteristics of the cloned DNA with the overall restriction fragment map generated a physical map of the genome. Some genes that have not been mapped because of a lack of mutants or leakiness at restrictive conditions were mapped by studying the in vitro protein synthesis of restriction endonuclease fragments.

Assembly of bacteriophage PRD1: particle formation with wild-type and mutant viruses

Bacteriophage PRD1 contains DNA, 17 proteins, and lipid. The assembly pathway involves the formation of empty particles that contain lipid and all of the proteins of mature virions, with the possible exception of one. The major and minor capsid proteins, P3 and P5, occur as soluble multimers before they appear in the empty particles. Nonsense mutants of PRD1 that involve structural proteins of the virion other than P3 form particles that are missing only the defective protein. Those mutants that are unable to form P3 do not form particles. Mutations in two other genes that code for nonstructural proteins (P10, which is membrane bound, and P17, which is soluble) result in the absence of particles. Protein P2 is necessary for adsorption to host cells. Protein P9 is necessary for particle filling with DNA, whereas P20 and P22 are necessary for stable DNA packaging. Electron micrographs of infected cells confirmed the gradient analysis of particle formation. No free vesicles were observed in mutants that could not form complete empty particles, indicating that there are no free intermediate particles before the empty virions.