Polyacrylic Acid Gel in Patients with Dry Eyes: A Randomised Comparison with Polyvinyl Alcohol

Purpose

To compare the safety and efficacy of polyacrylic acid 0.2% (PAA) gel and polyvinylalcohol 1.4% (PVA) in the treatment of patients with dry eyes.

Methods

Eighty-nine patients with dry eyes were randomly allocated to treatment with either PAA (48) or PVA (41) in a prospective, investigator-masked study in two centres. The parameters assessed were daily frequency of instillation of the study medications, ocular signs and symptoms, tear film break up time, Schirmer's test values, local tolerance and global assessment of the improvement following treatment.

Results

The two groups were similar in patient demographics and study parameters at baseline. The total score of symptoms (gritty or foreign body sensation, burning sensation, dry eye sensation, photophobia, others) and signs (conjunctival hyperaemia, ciliary injection, corneal and conjunctival epithelial staining) was reduced significantly more by treatment with PAA than with PVA at both three and six weeks (p<0.0001). The daily frequency of instillation of PAA was significantly less than that PVA on 38 of the 41 (93%) study days. Both PAA and PVA were safe and equally well-tolerated except for blurred vision, usually mild and transient, on PAA. On global assessment of the improvement in their dry eye condition, significantly more PAA patients felt better on treatment at six (p=0.02) weeks compared with those on PVA.

Conclusions

Polyacrylic acid gel was as safe as and more effective than polyvinylalcohol in the treatment of patients with dry eyes.

Delayed cerebral ischemia in aneurysmal subarachnoid hemorrhage: proposal of an evidence-based combined clinical and imaging reference standard

SUMMARY

Aneurysmal subarachnoid hemorrhage is associated with high morbidity and mortality, with delayed neurologic deficits from delayed cerebral ischemia contributing to a large portion of the adverse outcomes in this patient population. There is currently no consensus reference standard for establishing the diagnosis of delayed cerebral ischemia either in the research or clinical settings, ultimately limiting strategies for preventing delayed infarction and permanent neurologic deficits. There are currently both clinical and imaging-based criteria for the diagnosis of delayed neurologic deficits and vasospasm, respectively, however, neither clinical nor angiographic assessment alone has been shown to identify patients who develop adverse outcomes from delayed infarction. Thus, the purpose of this work is to propose a 3-tiered combined imaging and clinical reference standard based on evidence from the literature to standardize the diagnosis of delayed cerebral ischemia, both to allow consistency across research studies and to ultimately improve outcomes in the clinical setting.

Acid sensing ion channels and acid nociception

Acid Sensing Ion Channels (ASICs) are a family of cation channels expressed principally in neurons and that are activated by protons. The sensitivity of ASICs to acidosis and their distribution in primary sensory neurons points to a significant role of these channels in acid nociception. However, despite the fact that the first ASIC was identified more than 10 years ago the physiological and pathophysiological role of this channel family remains poorly understood. In this paper, the available body of data (genetic, pharmacological, and other) on ASICs will be reviewed and the role of ASIC in normal nociception and other pain sensations will be discussed. Some of the recent drug discovery and development activities ongoing in our laboratory, which point to ASICs being a relevant target for pain modulation, will also be summarized.

Hypophysectomy enhances interleukin-1beta, tumor necrosis factor-alpha, and interleukin-10 mRNA expression in the rat brain

Although the effects of various cytokines as regulators of hormone synthesis and production are well documented, the role for pituitary hormones as modulators of cytokine synthesis is not fully understood. In this study, we investigated the effect of pituitary hormones' depletion on cytokine synthesis after short- (21 days) and long- (35 days) term hypophysectomy (ST-HX and LT-HX, respectively). The expresssion of the proinflammatory cytokine interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) and the anti-inflammatory cytokines IL-10 and transforming growth factor-beta (TGF-beta) in the rat brain was studied using in situ hybridization. Our results indicate that IL-1beta mRNA-expressing cells were significantly upregulated at day 21 in hypophysectomized rats compared to sham-operated controls. This enhanced expression was also detected later at day 35 post hypophysectomy. However, TNF-alpha mRNA expression was significantly increased only at the later sampling interval. IL-10 mRNA-expressing cells were increased after long-term hypophysectomy compared to controls. TGF-beta mRNA-expressing cells were not increased after hypophysectomy. In conclusion, these results suggest a role for pituitary hormones in IL-1beta, TNF-alpha, and IL-10 synthesis.

Acute calcification in alkali-injured rabbit cornea treated with synthetic inhibitor of metalloproteinases (SIMP)

PURPOSE

The aim of this study was to evaluate the ultrastructure of acute calcification observed in alkali-injured rabbit corneas treated with synthetic inhibitor of metalloproteinases (SIMP).

METHODS

A 12-mm alkali burn was made on the right corneas of 16 rabbits. Eight eyes were treated with topical phosphate-buffered SIMP, and eight control eyes were given the buffer only. Six corneas (five in the SIMP group and one in the control group) developed chalky white opacification in the central area of the cornea within 6-30 days. The corneas were excised for the following examinations: (a) light microscopy, (b) energy-dispersive x-ray analysis, (c) electron microscopy, and (d) high-angle x-ray diffraction.

RESULTS

The results confirmed that there was stromal calcification in these corneas, as shown by positive van Kossa staining, needle-shaped calcium crystal aggregates, and increased calcium in the opaque areas of the corneas. Proteoglycans in the corneal stroma of both the SIMP group and the control group significantly decreased after alkali burns. Very few proteoglycan filaments could be identified in the calcified areas of the stroma. X-ray diffraction reflections with a Bragg spacing of 3.44 +/- 0.04 A were observed from all the calcified corneas treated with SIMP. The intermolecular spacings of collagen fibrils in the calcified stroma (1.24 +/- 0.34 nm) were significantly lower than those in the noncalcified stroma (1.64 +/- 0.04 nm) and the control corneas (1.64 +/- 0.02 nm). The results indicate that the collagen molecules within the fibrils of the calcified stroma are packed more closely than normal.

CONCLUSION

The comparison of the x-ray diffraction patterns from the calcified corneas and chicken bone suggests that the calcium deposits in these corneas are in a form similar to those found in bone. The higher rate and more extensive calcification in the SIMP-treated corneas may result from the inhibitory action of SIMP on debris processing, but the mechanism is unknown.

Hypercalcemia stimulates expression of intrarenal phospholipase A2 and prostaglandin H synthase-2 in rats. Role of angiotensin II AT1 receptors

In chronic hypercalcemia, inhibition of thick ascending limb sodium chloride reabsorption is mediated by elevated intrarenal PGE2. The mechanisms and source of elevated PGE2 in hypercalcemia are not known. We determined the effect of hypercalcemia on intrarenal expression of cytosolic phospholipase A2 (cPLA2), prostaglandin H synthase-1 (PGHS-1), and prostaglandin H synthase-2 (PGHS-2), enzymes important in prostaglandin production. In rats fed dihydrotachysterol to induce hypercalcemia, Western blot analysis revealed significant upregulation of both cPLA2 and PGHS-2 in the kidney cortex and the inner and outer medulla. Immunofluorescence localized intrarenal cPLA2 and PGHS-2 to interstitial cells of the inner and outer medulla, and to macula densa and cortical thick ascending limbs in both control and hypercalcemic rats. Hypercalcemia had no effect on intrarenal expression of PGHS-1. To determine if AT1 angiotensin II receptor activation was involved in the stimulation of cPLA2 and PGHS-2 in hypercalcemia, we treated rats with the AT1 receptor antagonist, losartan. Losartan abolished the polydipsia associated with hypercalcemia, prevented the increase in cPLA2 protein in all regions of the kidney, and diminished PGHS-2 expression in the inner medulla. In addition, losartan completely prevented the increase in urinary PGE2 excretion in hypercalcemic rats. Intrarenal levels of angiotensin II were unchanged in hypercalcemia. These data indicate that hypercalcemia stimulates intrarenal cPLA2 and PGHS-2 protein expression. Our results further support a role for angiotensin II, acting on AT1 receptors, in mediating this stimulation.

Stretch-induced atrial natriuretic factor release utilizes a rapidly depleting pool of newly synthesized hormone

Atrial muscle stretch is widely believed to be the main stimulus for atrial natriuretic factor (ANF) release. However, a few reports have shown that although stretch induces an immediate increase in ANF output, this release rapidly decays even though hormone stores are not significantly depleted. In the present work, this phenomenon was studied in an isolated rat atria preparation using double isotope labeling. The tissue was labeled with [14C]leucine for 3 h followed by a 1-h chase, and then with [3H]leucine for 1 h. A final 1-h chase period was conducted with the tissue under basal (0.2-g load) or stretched (5-g load) conditions. During this final chase period, the [14C]ANF represented older, stored ANF and the [3H]ANF represented the newly synthesized peptide. After both the [14C]- and [3H]leucine pulses, immunoprecipitable isotope incorporated into ANF appeared in the chase medium within the first 10 min and stabilized to lower levels after 20 min of chase. Stretch resulted in an immediate significant increase in immunoreactive ANF release and a decrease in the medium [14C]ANF specific activity (SA). However, no change was observed in the medium [3H]ANF SA but the tissue SA tended to decrease. It is concluded that a portion of ANF is immediately and preferentially released upon synthesis, while the remainder is taken up into tissue stores and released from them at a lower rate. The secretory response to stretch was demonstrated to consist of a rapid, short-lived burst of newly synthesized ANF, suggesting an increased translocation of newly synthesized hormone into a stretch-sensitive, rapidly depletable pool. Given the nature of this pool, additional factors yet to be characterized likely come into play to maintain chronically elevated circulating levels of ANF.

A decade of atrial natriuretic factor research

Present views on the biological significance of atrial natriuretic factor (ANF) relate this polypeptide hormone to the regulation of blood pressure and volume through its modulating effects on renal function, on blood vessel tone and permeability, and on the renin-angiotensin-aldosterone system. Although very important advances in the understanding of ANF have been made over the decade since its discovery, some fundamental facts about ANF biosynthesis and release remain to be elucidated. Stretch-induced enhancement of ANF release appears as the most significant mechanism underlying the endocrine response of the atria to acute volume load. This response decays over a period of minutes, indicating that chronic stimulation of ANF release involves mechanisms different from, or in addition to, those acting during acute stretch-stimulated release. In neither acute nor chronic conditions are the cellular or molecular mechanisms underlying ANF release understood. To better understand long-term stimulation of ANF release, we have conducted extensive in vitro testing of several hormones and neurotransmitters to determine their ability to modify ANF release. From these studies, clear-cut evidence of ANF stimulation was obtained with the vasopressor peptide endothelin. Investigations on the cell and molecular biology of cardiac muscle development and hypertrophy have shown that ANF is involved in cardiac growth. The role played by ANF in these processes is now being determined, but this is one line of evidence that suggests that this hormone, together with other natriuretic peptides, may have autocrine or paracrine functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Gamma aminobutyric acid (GABA), a modulator of anterior pituitary hormone secretion by hypothalamic and pituitary action

We have evaluated the role of GABA in the control of anterior pituitary (AP) hormone secretion by injecting it into the third ventricle of ovariectomized, ovariectomized-steroid primed and male rats. Specificity of the effects was determined by injecting the GABA blocker, bicuculline. The action of GABA directly on the pituitary was evaluated in vitro. The results indicate that intraventricular GABA can stimulate LH, growth hormone (GH) and, at high doses, prolactin (Prl) release, whereas low doses inhibit Prl and al doses inhibit TSH release. All of these actions are blocked by bicuculline. Intraventricular GABA administration is followed by an elevation of hypothalamic norepinephrine (NE) and median eminence dopamine (DA) levels and AP DA levels, which indicates that the compound stimulates both NE and DA release. The actions on GH and LH appear to proceed independently of DA, since the DA receptor blocker, pimozide, did not interfere with these effects, whereas the action to elevate Prl and to lower TSH was blocked by DA receptor blockade. Anterior pituitary hormone release by AP's incubated with GABA in vitro was unaltered except for an inhibition of Prl release by very high GABA doses, which could be blocked by bicuculline. Intravenous injection of bicuculline to assess the physiological significance of GABA in control of AP hormone secretion revealed no effect on FSH but a delayed rise in LH, an initial rise in Prl, followed by a fall, a tendency for GH values to rise and dramatic fall in TSH levels. These results suggest the possibility that GABA plays a physiological role in the control of AP hormone secretion, mainly via a hypothalamic action.