Ribosome-inactivating proteins up to date

Ribosome-inactivating proteins (RIPs) from plants inactivate eukaryotic ribosomes, as far as studied by rendering their 60 S subunit unable to bind elongation factor 2. These proteins seem widely distributed and possibly ubiquitous in plants. They are either type 1, those consisting of a single polypeptide chain, or type 2 (ricin and related toxins), those consisting of two chains, one of which is a galactose-binding lectin. The literature on RIPs from 1982 has been reviewed with respect to the chemical and biological properties of RIPs, their use for the preparation of immunotoxins and new perspectives.

Ribosome–Inactivating Proteins from Plants: Present Status and Future Prospects

Plant ribosome-inactivating proteins (RIPs) are N-glycosidases which cleave the N-glycosidic bond of adenine in a specific ribosomal RNA sequence. Most commonly RIPs are single-chain proteins (type 1 RIPs), but some (type 2 RIPs) possess a galactose-specific lectin domain that binds to cell surfaces. The latter RIPs are potent toxins, the best known of which is ricin. RIPs have antiviral and abortifacient activities, and, in a widespread application, can also be linked to antibodies or ligands to form immunotoxins or conjugates specifically toxic to a given type of cell.

Polynucleotide:adenosine glycosidase activity of ribosome-inactivating proteins: effect on DNA, RNA and poly(A)

Ribosome-inactivating proteins (RIP) are a family of plant enzymes for which a unique activity was determined: rRNAN-glycosidase at a specific universally conserved position, A4324in the case of rat ribosomes. Recently we have shown that the RIP from Saponaria officinalis have a much wider substrate specificity: they are actually polynucleotide:adenosine glycosidases. Here we extend studies on substrate specificity to most known RIP: 52 purified proteins, both type 1 (single-chain) and type 2 (two chain, an enzymatic chain and a lectin chain) were examined for adenine release on various substrates including RNAs from different sources, DNA, and poly(A). All RIP depurinated extensively DNA and some released adenine from all adenine-containing polynucleotides tested. From experimental evidence the entire class of plant proteins, up to now called ribosome-inactivating proteins, may be classified as polynucleotide:adenosine glycosidases. The newly identified substrates may be implicated in the biological role(s) of RIP.

Ribosome-inactivating proteins from the seeds of Saponaria officinalis L. (soapwort), of Agrostemma githago L. (corn cockle) and of Asparagus officinalis L. (asparagus), and from the latex of Hura crepitans L. (sandbox tree)

Ribosome-inactivating proteins, similar to those already known [Barbieri & Stirpe (1982) Cancer Surveys 1, 489-520] were purified from the seeds of Saponaria officinalis (two proteins), of Agrostemma githago (three proteins), and of Asparagus officinalis (three proteins), and from the latex of Hura crepitans (one protein). The yield ranged from 8 to 400 mg/100 g of starting material. All proteins have an Mr of approx. 30000 and an alkaline isoelectric point. Their sugar content varies from 0 (proteins from S. officinalis) to 40% (protein from H. crepitans). The ribosome-inactivating proteins inhibit protein synthesis by rabbit reticulocyte lysate, the ID50 (concentration giving 50% inhibition) ranging from 1 ng/ml (a protein from S. officinalis) to 18 ng/ml (a protein from A. githago). Those which were tested (the proteins from S. officinalis and from A. githago) also inhibit polymerization of phenylalanine by isolated ribosomes, acting in an apparently catalytic manner. The protein from H. crepitans inhibited protein synthesis by HeLa cells, with an ID50 of 4 micrograms/ml, whereas the proteins from S. officinalis and from A. githago had an ID50 of more than 50-100 micrograms/ml. The ribosome-inactivating proteins from S. officinalis and from A. githago reduced the number of local lesions by tobacco-mosaic virus in the leaves of Nicotiana glutinosa.

Purification and partial characterization of another form of the antiviral protein from the seeds of Phytolacca americana L. (pokeweed)

1. The pokeweed antiviral protein, previously identified in two forms (PAP and PAP II) in the leaves of Phytolacca americana (pokeweed) [Obrig. Irvin & Hardesty (1973) Arch. Biochem. Biophys. 155, 278-289; Irvin, Kelly & Robertus (1980) Arch. Biochem. Biophys. 200, 418-425] is a protein that prevents replication of several viruses and inactivates ribosomes, thus inhibiting protein synthesis. 2. PAP is present in several forms in the seeds of pokeweed. One of them, which we propose to call 'pokeweed antiviral protein from seeds' (PAP-S) was purified in high yield (180 mg per 100 g of seeds) by chromatography on CM-cellulose, has mol.wt. 30 000, and is similar to, but not identical with. PAP and PAP II. 3. PAP-S inhibits protein synthesis in a rabbit reticulocyte lysate with an ID50 (concentration giving 50% inhibition) of 1.1 ng/ml (3.6 x 10(-11) M), but has much less effect on protein synthesis by whole cells, with an ID50 of 1 mg/ml (3.3 x 10(-5) M), and inhibits replication of herpes simplex virus type 1.

Inhibition of protein synthesis in vitro by proteins from the seeds of Momordica charantia (bitter pear melon)

1. A haemagglutinating lectin was purified from the seeds of Momordica charantia by affinity chromatography on Sepharose 4B and on acid-treated Sepharose 6B. It has mol.wt. 115 000 and consists of four subunits, of mol.wts. 30 500, 29 000, 28 500 and 27 000. 2. The lectin inhibits protein synthesis by a rabbit reticulocyte lysate with an ID50 (concentration giving 50% inhibition) of approx. 5 micrograms/ml. Protein synthesis by Yoshida ascites cells is partially inhibited by the lectin at a concentration of 100 micrograms/ml. 3. From the same seeds another protein was purified which has mol.wt. 23 000 and is a very potent inhibitor of protein synthesis in the lysate system, with an ID50 of 1.8 ng/ml. This inhibitor has no effect on protein synthesis by Yoshida cells, and has no haemagglutinating properties. 4. Artemia salina ribosomes preincubated with the lectin or with the inhibitor lose their capacity to perform protein synthesis. The proteins seem to act catalytically, since they inactivate a molar excess of ribosomes. 5. The lectin and the inhibitor are somewhat toxic to mice, the LD50 being 316 and 340 micrograms/100 g body wt. respectively.

Distribution and properties of major ribosome-inactivating proteins (28 S rRNA N-glycosidases) of the plant Saponaria officinalis L. (Caryophyllaceae)

We have studied the distribution of the protein synthesis inhibitory activity in the tissues of Saponaria officinalis L. (Caryophyllaceae). Seven major saporins, ribosome-inactivating proteins, were purified to apparent homogeneity from leaves, roots and seeds using a new procedure of RIPs isolation including ion-exchange and hydrophobic chromatography. They all catalysed the depurination of rat liver ribosomes, which generate the Endo's diagnostic rRNA fragment upon treatment with acid aniline, thus indicating that A4324 from the 28S rRNA has been released (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912). The molecular mass of saporins by SDS-PAGE ranged between 30.2 and 31.6 kDa and by gel-filtration between 27.5 and 30.1 kDa. Amino acid composition and amino-terminal amino acid sequence indicate that all saporins may be considered isoforms. Only two saporins present in roots were glycosylated (SO-R1 and SO-R3). All saporins are very active on cell-free translation systems derived from rabbit reticulocyte lysates, rat liver, Triticum aestivum L., Cucumis sativus L. and Vicia sativa L. However, they are poor inhibitors of an Escherichia coli translation system. They inhibit protein synthesis in HeLa, BeWo and NB 100 cells, HeLa cells being the most resistant. The enzymatic activity of at least one saporin isoform was dependent on magnesium concentration in the standard rat liver cell-free system.

Sildenafil taken at bedtime significantly increases nocturnal erections: results of a placebo-controlled study

OBJECTIVES

Nighttime erections occur at all ages and contribute to the maintenance of the morphodynamic integrity of smooth muscle cells within the corpora cavernosa. This study was aimed at evaluating the effect on nocturnal erections of sildenafil versus a placebo taken at bedtime.

METHODS

A double-blind, crossover, placebo-controlled study design was used to examine the effects of sildenafil and placebo on sleep-related erectile activity. Thirty selected patients with erectile dysfunction (vasculogenic etiology, 22 patients [73%]; psychogenic etiology, 8 patients [27%]) were submitted to a polysomnographic recording of nocturnal erections, using a RigiScan device during 3 consecutive nights. After a first night of adaptation, the 2 following nights were used to study patients after the administration of sildenafil (100 mg) or a placebo taken at bedtime.

RESULTS

Twenty-three patients (77%) showed a significantly improved nocturnal erectile activity (according to the calculation of rigidity and tumescence activity units) after the administration of sildenafil (P <0.01), 5 patients (17%) showed comparable nocturnal erections with sildenafil and placebo, and 2 patients (6%) showed a significantly improved nocturnal erectile activity after taking the placebo (P <0.05). Overall, mean rigidity and tumescence activity values at the tip and base of the penis were significantly improved after sildenafil rather than placebo administration (P <0.001). The duration of tip rigidity greater than 60% was significantly longer during the night with sildenafil (P <0. 001). Although the number of erectile episodes was greater during the sildenafil night, this did not reach statistical significance.

CONCLUSIONS

In most patients with good sleep efficiency and who have erectile dysfunction, sildenafil, rather than a placebo, taken at bedtime produces a significantly improved nocturnal erectile activity. Further studies are needed to verify whether this preliminary finding may constitute the basis for the use of sildenafil as a tool for preventing erectile dysfunction.

Impact of gender difference on vitamin D status and its relationship with the extent of coronary artery disease

BACKGROUND AND AIM

There has been a surge of interest in the cardiovascular effects of vitamin D (25(OH)D), preventing the processes leading to vascular wall degeneration and coronary artery disease (CAD). Gender differences have been suggested for vitamin D status, with a higher rate of deficiency occurring especially in post-menopausal women, increasing the risk of bone fractures and osteoporosis. However, to date, few studies have evaluated the differences in 25(OH)D levels according to gender and their impact on the extent of CAD, which was therefore the aim of the present study.

METHODS AND RESULTS

In patients undergoing coronary angiography, fasting samples were collected for the assessment of 25(OH)D levels. Significant CAD was defined as at least one vessel stenosis >50%, while severe CAD was defined as left main and/or three-vessel disease. Of the 1811 patients included, 530 (29.3%) were females, who displayed older age (p < 0.001), higher rate of renal failure (p < 0.001), hypertension (p = 0.05), treatment with angiotensin-receptor blockers (p = 0.03) and diuretics (p < 0.001), acute presentation (p < 0.001), higher platelet count (p < 0.001), glycosylated haemoglobin (p = 0.02) and cholesterol (p = 0.001), but an inverse relationship with smoking (p < 0.001), previous cardiovascular events (p < 0.001), treatment with statins and acetylsalicylic acid (ASA) (p < 0.001), body mass index (p = 0.002), haemoglobin (p < 0.001), leucocytes (p = 0.03) and triglycerides (p < 0.001). Female gender was associated with lower vitamin D levels (14.5 ± 10.9 vs. 15.9 ± 9.5, p = 0.007) and independently associated with severe vitamin D deficiency (41.9% vs. 30.4%, p < 0.001; adjusted odds ratio (OR) (95% confidence interval (CI)) = 1.42 (1.08-1.87), p = 0.01). Lower tertiles of vitamin D were associated with an increased prevalence and severity of CAD in females (adjusted OR (95% CI = 1.26 (1.10-1.44), p = 0.001 for CAD; adjusted OR (95% CI) = 1.6 (1.39-1.87), p < 0.001 for severe CAD). In males, vitamin D status was independently related to the prevalence (adjusted OR (95% CI) = 1.28 (1.02-1.61), p = 0.03) of CAD, but not the extent of CAD (adjusted OR (95% CI) = 1.02 (0.86-1.2), p = 0.84).

CONCLUSION

Gender significantly affects vitamin D status. The lower 25(OH)D levels observed in females, as compared to males, play a more relevant role in conditioning the severity of CAD.

Trichosanthin, alpha-momorcharin and beta-momorcharin: identity of abortifacient and ribosome-inactivating proteins

The abortifacient proteins trichosanthin, alpha-momorcharin and beta-momorcharin at nM concentrations inhibit cell-free protein synthesis. The momorcharins and the ribosome-inactivating proteins isolated from Momordica charantia seeds cross-react with the respective antisera. The ribosome-inactivating proteins saporins, pokeweed antiviral protein (PAP) and, to a lesser extent, gelonin have abortifacient activity on pregnant mice.

Systematic review and meta-analysis: Efficacy and safety of POEM for achalasia

BACKGROUND

Peroral endoscopic esophageal myotomy (POEM) represents a less invasive alternative, as compared with conventional laparoscopic Heller myotomy for treating achalasia patients. In the last years, a number of prospective and retrospective experiences with POEM use for achalasia have been published.

METHODS

Relevant publications in which patients affected by achalasia underwent POEM treatment were identified by PubMed databases for the period 2010 - 2013. From each study, we extracted the number and type of major complications (defined as those requiring any additional medical or surgical intervention). Data were pooled, using random-effects models. Heterogeneity among studies was assessed by using Cochran's Q and the I (2) statistic.

RESULTS

We found 16 studies that provided data on 551 patients. The median surveillance period was 6 months (range: 3-12). The median of mean POEM duration was 156 minutes (range: 42-112). Median myotomy length was 10 cm (range: 6-14). Technical and clinical success were reported in 97% (95% CI: 94-98%) and 93% (407/428; 95% CI: 90-95%). No heterogeneity (I (2 )= 0%) or publication bias was present in both estimates. When limiting the analysis only to adverse events that require medical or surgical interventions, major adverse events occurred in 14% (95% CI: 11-17%); however, only one patient needed post-POEM surgery (0.2%; 95% CI: 0-0.5%).

CONCLUSIONS

POEM appeared to be a highly feasible and effective endoscopic treatment for achalasia. Despite POEM being apparently associated with relatively high morbidity, most patients are successfully managed conservatively, so that POEM appears as a very safe procedure; however, POEM should only be performed in centers able to treat POEM complications, such as pneumothorax or pneumoperitoneum.

Polynucleotide: adenosine glycosidase activity of saporin-L1: effect on DNA, RNA and poly(A)

The ribosome-inactivating proteins (RIPs) are a family of plant enzymes for which a unique activity has been determined: rRNA N-glycosidase, which removes adenine at a specific universally conserved position (A4324 in the case of rat ribosomes). Here we report that saporin-L1, a RIP from the leaves of Saponaria officinalis, recognizes other substrates, including RNAs from different sources, DNA and poly(A). Saporin-L1 depurinated DNA extensively and released adenine from all adenine-containing polynucleotides tested. Adenine was the only base released from DNA or artificial polynucleotides. The characteristics of the reactions catalysed by saporin-L1 have been determined: optimal pH and temperature, ionic requirements, and the kinetic parameters Km and kcat. The reaction proceeded without cofactors, at low ionic strength, in the absence of Mg2+ and K+. Saporin-L1 had no activity towards various adenine-containing non-polynucleotide compounds (cytokinins, cofactors, nucleotides). This plant protein may now be classified as a polynucleotide: adenosine glycosidase.

Activities associated with the presence of ribosome-inactivating proteins increase in senescent and stressed leaves

The ribosome-inactivating proteins (RIPs) from Hura crepitans and Phytolacca americana release adenine from herring sperm DNA. Leaf extracts from these plants show the same enzymatic activities as the RIPs. The translation inhibitory activity and the activity on DNA are both increased in the leaves of both plants during senescence or when subjected to heat or osmotic stress. It is proposed that a physiological role of RIPs could be to intervene in the death of plant cells.

Long-term observational study of afamelanotide in 115 patients with erythropoietic protoporphyria

BACKGROUND

In erythropoietic protoporphyria (EPP), an inherited disease of porphyrin-biosynthesis, the accumulation of protoporphyrin in the skin causes severely painful phototoxic reactions. Symptom prevention was impossible until recently when afamelanotide became available. Afamelanotide-induced skin pigmentation has statistically significantly improved light-tolerance, although the clinical significance of the statistical effect was unknown.

OBJECTIVES

To assess clinical effectiveness by recording compliance and safety during prolonged use.

METHODS

We report longitudinal observations of 115 ambulatory patients with EPP, who were treated with a total of 1023 afamelanotide implants over a period of up to 8 years at two porphyria centres; one in Rome, Italy, and the other in Zurich, Switzerland.

RESULTS

Since the treatment first became available in 2006, the number of patients treated with 16 mg afamelanotide implants rose continuously until June 2014, when 66% of all patients with EPP known to the porphyria centres were treated. Only three patients considered afamelanotide did not meet their expectations for symptom improvement; 23% discontinued the treatment for other, mostly compelling, reasons such as pregnancy or financial restrictions. The quality of life (QoL) scores, measured by an EPP-specific questionnaire, were 31 ± 24% of maximum prior to afamelanotide treatment, rose to 74% after starting afamelanotide and remained at this level during the entire observation period. Only minor adverse events attributable to afamelanotide, predominantly nausea, were recorded.

CONCLUSION

Based on the improved QoL scores, high compliance and low discontinuation rates, we conclude that afamelanotide exhibits good clinical effectiveness and good safety in EPP under long-term routine conditions.

Inhibition of protein synthesis by carbonyl compounds (4-hydroxyalkenals) originating from the peroxidation of liver microsomal lipids

Carbonyl compounds released during the NADPH-Fe dependent peroxidation of liver microsomal lipids and identified as 4-hydroxyalkenals (almost entirely as 4-hydroxynonenal) inhibit protein synthesis in a rabbit reticulocyte lysate. The ID50 was 0.48 mM. The inhibitory effect was reproduced by synthetic 4-hydroxynonenal. The inhibition was already evident at 1-2 min of incubation. The addition of -SH groups to the incubation medium afforded a marked protection against the inhibition of protein synthesis. The inhibitory effect seems to be due to an interaction of the carbonyl compound with -SH groups essential for the cellular protein synthetic machinery.

Impact of diabetes on neutrophil-to-lymphocyte ratio and its relationship to coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is the leading cause of mortality among diabetic patients, and the neutrophil-to-lymphocyte ratio (NLR) has recently emerged from among inflammatory parameters as a potential indicator of vascular complications and poorer outcome in patients with diabetes. This study aimed to evaluate: 1) the impact of diabetes on NLR; and 2) the role of NLR on the extent of CAD among diabetic patients undergoing coronary angiography.

METHODS

Consecutive patients undergoing coronary angiography were included. Diabetic status and main chemistry parameters were assessed at the time of admission. Significant CAD was defined as at least one vessel with stenosis>50%, while severe CAD was left main and/or three-vessel disease, as evaluated by quantitative coronary angiography (QCA).

RESULTS

Diabetes was observed in 1377 of 3756 patients (36.7%); they were older, and displayed higher-risk cardiovascular profile and more complex CAD. Diabetic status was also associated with a significant increase in NLR (P=0.004). Among diabetics, higher NLR tertile values were related to ageing (P<0.001), dyslipidaemia (P<0.001), renal failure (P<0.001), body mass index (P<0.001), previous percutaneous coronary revascularization (P=0.004) and cerebrovascular events (P=0.003), acute presentation (P<0.001), treatment at admission with beta-blockers/statins/ASA (all P<0.001), diuretics (P=0.01) or clopidogrel (P=0.04), platelet count (P=0.03), white blood cell count, creatinine, glycaemia and C-reactive protein (P<0.001), and inversely related to haemoglobin, triglyceride levels (P<0.001) and smoking (P=0.03). NLR was associated with multivessel disease (P<0.001), degree of stenosis (P=0.01), type C lesions (P=0.02), coronary calcifications and intracoronary thrombus (P<0.001), but inversely with in-stent restenosis (P=0.003) and TIMI flow grade (P=0.02). Also, NLR was directly related to CAD prevalence (P<0.001; adjusted OR [95% CI]: 1.62 [1.27-2.07], P<0.001) and CAD severity (P<0.001; adjusted OR [95% CI]: 1.19 [1.00-1.43], P=0.05).

CONCLUSION

NLR is increased among diabetic patients and, in such patients, is independently associated with the prevalence and severity of CAD. Further studies are now needed to confirm present results and to evaluate the underlying pathophysiological mechanisms behind our findings.

Inhibition of protein synthesis in vitro by a lectin from Momordica charantia and by other haemagglutinins

Protein synthesis by a rabbit reticulocyte lysate is inhibited by the haemagglutinating lectins from Momordica charantia and Crotalaria juncea seeds and from the roe of Rutilus rutilus, and by a commercial preparation of the mitogenic lectin from Phytolacca americana. The haemagglutinins from the seeds of Ricinus communis and of Vicia cracca acquired inhibitory activity after their reduction with 2-mercaptoethanol.

Bryodin, a ribosome-inactivating protein from the roots of Bryonia dioica L. (white bryony)

Bryodin is a strongly basic (pI greater than or equal to 9.5) glycoprotein (neutral sugar content 6.3%) with Mr 30,000, purified from the roots of Bryonia dioica (white bryony). This protein inhibits protein synthesis by a rabbit reticulocyte lysate with and ID50 (concentration causing 50% inhibition) of 0.12 nM (3.6 ng/ml) and has much less effect on protein synthesis by whole cells, with ID50 values ranging from 46 nM to 2.27 microM (1.4-67 micrograms/ml). Bryodin acts by inactivating ribosomes, with a less-than-equimolar ratio, which suggests a catalytic action. Bryodin decreases the number of local lesions induced by tobacco mosaic virus in the leaves of Nicotiana glutinosa. From all its properties, bryodin can be considered to be a ribosome-inactivating protein, similar to those already known [reviews: Barbieri & Stirpe (1982) Cancer Surveys 1, 489-520; Stirpe & Barbieri (1986) FEBS Lett. 195, 1-8].

Purification and properties of new ribosome-inactivating proteins with RNA N-glycosidase activity

Ribosome-inactivating proteins (RIPs) similar to those already known (Stirpe & Barbieri (1986) FEBS Lett. 195, 1-8) were purified from the seeds of Asparagus officinalis (two proteins, asparin 1 and 2), of Citrullus colocynthis (two proteins, colocin 1 and 2), of Lychnis chalcedonica (lychnin) and of Manihot palmata (mapalmin), from the roots of Phytolacca americana (pokeweed antiviral protein from roots, PAP-R) and from the leaves of Bryonia dioica (bryodin-L). The two latter proteins can be considered as isoforms, respectively, of previously purified PAP, from the leaves of P. americana, and of bryodin-R, from the roots of B. dioica. All proteins have an Mr at approx, 30,000, and an alkaline isoelectric point. Bryodin-L, colocins, lychnin and mapalmin are glycoproteins. All RIPs inhibit protein synthesis by a rabbit reticulocyte lysate and phenylalanine polymerization by isolated ribosomes and alter rRNA in a similar manner as the A-chain of ricin and related toxins (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912).

Characterization of a Saponaria officinalis seed ribosome-inactivating protein: immunoreactivity and sequence homologies

A ribosome inactivating protein from Saponaria officinalis, SO-6, was purified and the N-terminus sequenced. The sequence shows extensive homology with Pokeweed antiviral protein, Pokeweed antiviral protein II, Pokeweed antiviral seed protein and dodecandrin. SDS gel electrophoresis in the Laemmli system revealed two bands of similar intensities with a smear between them, probably an artifact due to the high pI of the protein. Use of a harsher denaturing gel system resulted in one band in electrophoresis. Immune antisera was raised in rabbits against this protein and it cross reacted with other proteins (SO-5, SO-8 and SO-9) from seeds of Saponaria officinalis, but not with gelonin, Momordica charantia inhibitor and dianthin 32.

Effect of yohimbine-trazodone on psychogenic impotence: a randomized, double-blind, placebo-controlled study

OBJECTIVES

The aim of this study was to determine the effectiveness and safety of yohimbine and trazodone used together for the treatment of pure psychogenic impotence.

METHODS

Sixty-three patients who had psychogenic impotence diagnosed on the basis of sexual history, results of physical examination, laboratory analysis, polysomnographic recording of nocturnal erections, and dynamic color Doppler sonography of the cavernosal arteries were entered into a randomized, double-blind, placebo-controlled, partial crossover study comparing placebo with yohimbine (15 mg per day orally) and trazodone (50 mg per day orally) used together. Treatment consisted of two 8-week courses. Patients who initially received placebo for 8 weeks were then switched to the 2-drug combination for 8 weeks. Erectile function, ejaculation, interest in sex, and sexual thoughts were investigated at the end of drug treatment and at 3- and 6-month follow-up. For statistical analysis chi-square, McNemar, and Student's t test for unpaired data were used.

RESULTS

Fifty-five patients (87%) completed the whole treatment schedule. Positive clinical results (complete and partial responses) were obtained in 39 (71%) patients at the end of the drug treatment phase. These results were significantly better than those obtained with placebo (p < 0.01). Positive results were maintained in 32 (58%) and 31 (56%) patients at 3- and 6-month follow-up, respectively. Minor drug-related adverse effects occurred in 6 (11%) of the patients in the yohimbine-trazodone group and in 2 (4%) in the placebo group.

CONCLUSIONS

The combination of yohimbine and trazodone is a safe and effective first-line treatment for psychogenic impotence.

Some ribosome-inactivating proteins depurinate ribosomal RNA at multiple sites

Saporin-S6, a ribosome-inactivating protein (RIP) from Saponaria officinalis released more than 1 mol of adenine/mol of ribosomes from house fly (Musca domestica) larvae and from rat liver. The release of adenine from rat liver ribosomes by several RIPs (plant enzymes with RNA N-glycosidase activity) was examined. Saporins, pokeweed antiviral protein from roots of Phytolacca americana (PAP-R), and trichokirin from Trichosanthes kirilowii seeds depurinated rat liver ribosomes at more than one site. Up to 33 mol of adenine were released from 1 mol of ribosomes. This property is not common to all RIPS.

Effect of ribosome-inactivating proteins on virus-infected cells. Inhibition of virus multiplication and of protein synthesis

HEp-2 cells were infected with herpes simplex virus-1 (HSV-1) or with polio-virus I in the presence of plant proteins which inactivate ribosomes in cell-free systems, while exerting scarce effect on whole cells. Ribosome-inactivating proteins used were gelonin, from seeds of Gelonium multiflorum, an inhibitor from the seeds of Momordica charantia, dianthin 32, from the leaves of Dianthus caryophyllus (carnation), and PAP-S, from the seeds of Phytolacca americana (pokeweed). All proteins tested had the following effects: 1. They reduced viral yield; 2. They decreased HSV-1 plaque-forming efficiency; 3. They inhibited protein synthesis more in infected than in uninfected cells. These results strongly suggest that ribosome-inactivating proteins impair viral replication by inhibiting protein synthesis in virus-infected cells, in which presumably they enter more easily than in uninfected cells.