Effects of phosphodiesterase type 5 inhibitors on choroid and ocular vasculature: a literature review.

To provide information on the effects of phosphodiesterase type 5 (PDE5) inhibitors on choroidal vessels and central serous chorioretinopathy (CSC) and possible implications for development of exudative age-related macular degeneration (AMD). Two independent investigators conducted a qualitative review of PubMed to identify studies on the choroidal effect of PDE5 inhibitors in June 2019. The search used key words that included PDE5 inhibitors, sildenafil, tadalafil, vardenafil, choroid, choroidal flow, choroidal vessels, choroidal thickness, CSC, AMD or a combination. Only studies which assessed choroidal findings were included. Many ocular diseases are related to changes in choroidal thickness and perfusion. Patients with AMD, who have decreased choroidal perfusion, may manifest more severely diminished choroidal ability to deliver oxygen and other metabolites to the retina, leading to growth of neovascular tissue. As a result of this engorgement of the choroidal vasculature, some patients may have leakage across the retinal pigment epithelium (RPE) and accumulation of subretinal fluid, resulting in CSC. Transient visual symptoms, i.e., changes in color perception and increased light sensitivity, are well-known adverse effects, but there have been rare reports of vision-threatening ocular complications in users of PDE5 inhibitors, such as nonarteritic anterior ischemic optic neuropathy and cilioretinal artery occlusion. The choroid is a vascular tissue analogous in many respects to the corpus cavernosum, and PDE5 inhibitors may increase the choroidal thickness and perfusion. While it is intuitively obvious that thickness of the choroid alone does not guarantee better choriocapillaris oxygenation, it is a reasonable step towards ameliorating ischemia. These drugs have numerous physiologic effects on the choroid related to blood flow, such as clinical consequences in CSC and AMD.

Purification and characterization of Plasmodium falciparum hypoxanthine-guanine-xanthine phosphoribosyltransferase and comparison with the human enzyme.

The human malaria parasite Plasmodium falciparum is auxotrophic for purines and relies on the purine salvage pathway for the synthesis of its purine nucleotides. Hypoxanthine-guanine-xanthine phosphoribosyltransferase (HGXPRT) is a key purine salvage enzyme in P. falciparum, making it a potential target for chemotherapy. Previous attempts to purify this enzyme have been unsuccessful because of the difficulty in obtaining cultured parasite material and because of the inherent instability of the enzyme during purification and storage. Other groups have tried to express recombinant P. falciparum HGXPRT but only small amounts of activity were obtained. The successful expression of recombinant P. falciparum HGXPRT in Escherichia coli has now been achieved and the enzyme purified to homogeneity in mg quantities. The measured molecular mass of 26 229+/-2 Da is in excellent agreement with the calculated value of 26232 Da. A method to stabilise the activity and to reactivate inactive samples has been developed. The subunit structure of P. Jilciparum HGXPRT has been determined by ultracentrifugation in the absence (tetramer) and presence (dimer) of KC1. Kinetic constants were determined for 5-phospho-alpha-D-ribosyl-1-pyrophosphate, for the three naturally-occurring 6-oxopurine bases guanine, hypoxanthine, and xanthine and for the base analogue, allopurinol. Differences in specificity between the purified P. falciparum HGXPRT and human hypoxanthine guanine phosphoribosyltransferase enzymes were detected which may be able to be exploited in rational drug design.

Mutational analysis of the cystathionine beta-synthase gene: a splicing mutation, two missense mutations and an insertion in patients with homocystinuria. Mutations in brief no. 120. Online.

RT-PCR and direct sequence analyses were used to define mutations in the cystathionine beta-synthase (CBS) gene in two unrelated male patients with vitamin B6 nonresponsive homocystinuria. Both patients were compound heterozygotes for CBS alleles containing point mutations. One patient had a maternally derived G->A transition in the splice-donor site of intron 1, resulting in aberrant splicing of CBS mRNA. The other allele contained a missense mutation resulting in the previously reported E144K mutant CBS protein. The second patient had a maternally derived 4 bp insertion in exon 17, predicted to cause a CBS peptide of altered amino acid sequence. A 494G->A transition was found in exon 4 of the other allele, predicting a C165Y substitution. Expression of recombinant CBS protein, containing the C165Y mutation, had no detectable catalytic activity. Each mutation was confirmed in genomic DNA.

Characterisation of five missense mutations in the cystathionine beta-synthase gene from three patients with B6-nonresponsive homocystinuria.

Homocystinuria, due to a deficiency of the enzyme cystathionine beta-synthase (CBS), is an inborn error of sulphur-amino acid metabolism. This is an autosomal recessive disease which results in hyperhomocysteinaemia and a wide range of clinical features, including optic lens dislocation, mental retardation, skeletal abnormalities and premature thrombotic events. We report the identification of 5 missense mutations in the protein-coding region of the CBS gene from 3 patients with pyridoxine-nonresponsive homocystinuria. Reverse-transcription PCR was used to amplify CBS cDNA from each patient and the coding region was analysed by direct sequencing. The mutations detected included 3 novel (1058C-->T, 992C-->A and 1316G-->A) and 2 previously identified (430G-->A and 833C-->T) base alterations in the CBS cDNA. Each of these mutations predicts a single amino acid substitution in the CBS polypeptide. Appropriate cassettes of patient CBS cDNA, containing each of the above defined mutations, were used to replace the corresponding cassettes of normal CBS cDNA sequence within the bacterial expression vector pT7-7. These recombinant mutant and normal CBS constructs were expressed in Escherichia coli cells and the catalytic activities of the mutant proteins were compared with normal. All of the mutant proteins exhibited decreased catalytic activity in vitro, which confirmed the association between the individual mutation and CBS dysfunction in each patient.

Recruitment and retention of psychiatrists in non-metropolitan public positions in Queensland: research on "Queensland Health's response'.

OBJECTIVE: To evaluate Queensland Health's recruitment campaign of 15 fulltime psychiatrists to non-metropolitan areas between July 1992 and December 1993. METHOD: A detailed 170-item Likert-type questionnaire was designed and mailed to all 15 psychiatrists. Thirteen questionnaires were completed and followed-up by a face to face interview. RESULTS: Findings indicate that most of those recruited were experienced senior specialists who came to the positions as result of personal contact and were attracted to non-metropolitan positions because of 'lifestyle' and professional challenge' variables. 'Lifestyle' and 'professional' variables were identified as major contributors to their retention. They reported that 'bureaucracy' and 'social and family' reasons would be the most likely cause of them considering leaving their current positions. CONCLUSIONS: While the recruitment campaign was evaluated as successful, some aspects were clearly more influential than others. It was noted that factors which were likely to influence psychiatrists to leave non-metropolitan public sector positions were more 'public' than 'non-metropolitan' in nature.

Variable hyperhomocysteinaemia phenotype in heterozygotes for the Gly307Ser mutation in cystathionine beta-synthase.

BACKGROUND: A deficiency of cystathionine beta-synthase (CBS) activity is the most frequent cause of homocystinuria, an autosomal recessive disease with multiple clinical manifestations. Mutations in the CBS gene have been reported in several patients with homocystinuria. AIMS: To establish the molecular basis of CBS deficiency in a female patient with pyridoxine non-responsive homocystinuria, and to apply the findings to genetic screening of her family members. METHODS: The entire coding region of the CBS cDNA was amplified by PCR and used for direct sequence analysis. Mutant alleles were confirmed by direct sequence analysis of PCR-amplified genomic DNA, and by a combination of single strand conformation polymorphism and temperature gradient gel electrophoresis analysis. RESULTS: The proband was homozygous for a G919A base transition which predicts the substitution of serine for glycine at codon 307 in the CBS protein (G307S). The parents (both of Irish background) were heterozygotes for the G307S allele, while an asymptomatic sibling had normal CBS sequence, Plasma homocysteine, assessed after an oral methionine load, indicated the mother clearly had moderate hyperhomocysteinaemia, whereas the father had normal concentrations of homocysteine. This is the first report of a normal methionine load test in a proven heterozygote for a CBS mutation which causes severe homocystinuria in the homozygote. Other factor(s) may have contributed to hyperhomocysteinaemia in the mother. The G307S allele has been reported in other patients and appears to be a common allele among families of Celtic origin.

The management of gout.

We now have sufficient knowledge to be able to identify the factors contributing to hyperuricemia in most patients with gout. Some of these factors, such as obesity, a high-purine diet, regular alcohol consumption, and diuretic therapy, may be correctable. In patients with persistent hyperuricemia, regular medication should lower the serum urate concentration to an optimal level. The continuing challenge is to educate patients about correctable factors and the importance of regular medication and ensure their compliance so that attacks of gout do not recur.

Queensland's geographical maldistribution of psychiatrists and Queensland Health's response.

There is a major geographical maldistribution and shortage of psychiatrists throughout Queensland. In June 1992, 48 psychiatrists worked outside of Brisbane where 66% of the population reside, while 172 psychiatrists worked in the metropolitan area. The reasons for and the effects of the maldistribution are discussed. Since 1991, Queensland Health has developed a number of key strategies to attract and retain psychiatrists in our non-metropolitan areas. These strategies are outlined. Between July 1992 and December 1993, 14 new full time psychiatrists were recruited. The results of these strategies are encouraging.

Train suicides in Brisbane, Australia, 1980-1986.

Train suicides have not been widely studied, but this mode of suicide is one which results in high mortality and disfigurement, considerable trauma to bereaved relatives, and often considerable psychological difficulties for those indirectly involved such as train drivers and onlookers. The placement of psychiatric hospitals close to railways and the advisability of erecting barriers have sometimes been hotly debated. This survey of 23 train suicides in Brisbane, Australia, addresses these issues. It shows that 57% of the victims had been treated for schizophrenia, and 57% were also psychiatric inpatients at the time of the incident. Forty eight percent of the deaths occurred close to the regional psychiatric hospital. Fifty two percent were young adults aged 15-29 years. All suicides occurred during daylight or within 2 h of sunset. These results are similar to those from another study in the same city which implicated schizophrenia in jumping from heights--also a grossly self-mutilating behavior. The erection of barriers to reduce mortality from train suicide was not considered a feasible solution for Brisbane, but other cities might benefit from such measures.

A review of the molecular basis of hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency.

Hypoxanthine-guanine phosphoribosyltransferase (HPRT, EC 2.4.2.8) is a purine salvage enzyme that catalyses the conversion of hypoxanthine and guanine to their respective mononucleotides. Partial deficiency of this enzyme can result in the overproduction of uric acid leading to a severe form of gout, whilst a virtual absence of HPRT activity causes the Lesch-Nyhan syndrome which is characterised by hyperuricaemia, mental retardation, choreoathetosis and compulsive self-mutilation. The HPRT-encoding gene is located on the X chromosome in the region q26-q27 and consists of nine exons and eight introns totalling 57 kb. This gene is transcribed to produce an mRNA of 1.6 kb, which contains a protein encoding region of 654 nucleotides. With the advent of increasingly refined techniques of molecular biology, it has been possible to study the HPRT gene of individuals with a deficiency in HPRT activity to determine the genetic basis of the enzyme deficiency. Many different mutations throughout the coding region have been described, but in the absence of precise information on the three-dimensional structure of the HPRT protein, it remains difficult to determine any consistent correlation between the structure and function of the enzyme.

Genetic control of the renal clearance of urate: a study of twins.

Although a genetic predisposition to gout has been recognised for centuries, its mechanism has never been defined. This study was designed to determine whether this factor might be the renal clearance of urate, which is an important determinant of the concentration of urate in serum. In this study the renal clearance of urate was examined in 37 pairs of normouricaemic twins to determine whether this resemblance was genetically mediated. Monozygotic twins had more similar values of urate clearance and fractional excretion of urate than dizygotic twins. The heritability of the renal clearance of urate was estimated as about 60% (95% confidence limits 40 to 100%), whereas the heritability of the fractional excretion of urate was 87% (confidence limits 45 to 100%). This study supports the hypothesis that genetic factors exert an important control on the renal clearance of urate, which determines some of the familiarity of hyperuricaemia and gout.

Gout due to renal disease.

From 120 patients attending a referral gout clinic, 12 patients were found to have primary renal disease at the time of, or prior to, their first attack of acute gouty arthritis. This number excluded those with chronic lead nephropathy, polycystic kidneys or who were receiving diuretics. The nature of the renal disease was usually of the tubulointerstitial variety rather than of glomerular origin. The renal clearance of urate per unit of glomerular filtration rate, which usually increases with renal disease, was generally reduced, suggesting impairment of renal excretion of urate. Nine of the patients were female (four premenopausal) and only three were males. The degree of renal impairment was only mild to moderate. Other common associations with gout, such as obesity, hypertension and regular alcohol consumption, were not prominent. The intrinsic renal disease in these patients was considered to be the major contributor to their development of hyperuricaemia and gout.

The molecular characterisation of HPRT CHERMSIDE and HPRT COORPAROO: two Lesch-Nyhan patients with reduced amounts of mRNA.

A complete deficiency of the purine salvage enzyme, hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8), in man results in the Lesch-Nyhan (LN) syndrome. Two unrelated patients with the full LN syndrome showed no evidence of a major alteration to the gene encoding HPRT (HPRT) by restriction endonuclease analysis, but exhibited negligible levels of HPRT mRNA on Northern blots. DNA from these patients was characterised further. Amplification, by the polymerase chain reaction (PCR), of individual HPRT-exon fragments from genomic DNA followed by nucleotide (nt) sequence analysis using automated technology, revealed single-base mutations in each patient. One patient has an insertion of a T within exon-2, which places a stop codon in frame, presumably resulting in premature termination of translation of the HPRT mRNA. The other patient has a G----A base substitution at the 5' end of intron-6, at the junction of exon-6 and intron-6. Although dot blot analysis indicated negligible HPRT mRNA in lymphoblast cells from both patients, we were successful in amplifying HPRT cDNA using PCR. Direct nt sequence analysis of the amplified cDNA confirmed the insertion of a T in exon-2 in the one patient and revealed a complete deletion of exon-6 in the other patient, the latter event presumably arising due to aberrant splicing of primary message. Both mutations were also confirmed by hybridisation of amplified genomic DNA with allele-specific oligodeoxyribonucleotide probes. This study illustrates two approaches for analysing DNA mutations at the molecular level and demonstrates the power of PCR technology in the study of genetic diseases.(ABSTRACT TRUNCATED AT 250 WORDS)