Comparison of the isomerization mechanisms of human melanopsin and invertebrate and vertebrate rhodopsins

Comparative modeling and ab initio multiconfigurational quantum chemistry are combined to investigate the reactivity of the human nonvisual photoreceptor melanopsin. It is found that both the thermal and photochemical isomerization of the melanopsin 11-cis retinal chromophore occur via a space-saving mechanism involving the unidirectional, counterclockwise twisting of the =C11H-C12H= moiety with respect to its Lys340-linked frame as proposed by Warshel for visual pigments [Warshel A (1976) Nature 260(5553):679–683]. A comparison with the mechanisms documented for vertebrate (bovine) and invertebrate (squid) visual photoreceptors shows that such a mechanism is not affected by the diversity of the three chromophore cavities. Despite such invariance, trajectory computations indicate that although all receptors display less than 100 fs excited state dynamics, human melanopsin decays from the excited state ∼40 fs earlier than bovine rhodopsin. Some diversity is also found in the energy barriers controlling thermal isomerization. Human melanopsin features the highest computed barrier which appears to be ∼2.5 kcal mol⁻¹ higher than that of bovine rhodopsin. When assuming the validity of both the reaction speed/quantum yield correlation discussed by Warshel, Mathies and coworkers [Weiss RM, Warshel A (1979) J Am Chem Soc 101:6131–6133; Schoenlein RW, Peteanu LA, Mathies RA, Shank CV (1991) Science 254(5030):412–415] and of a relationship between thermal isomerization rate and thermal activation of the photocycle, melanopsin turns out to be a highly sensitive pigment consistent with the low number of melanopsin-containing cells found in the retina and with the extraretina location of melanopsin in nonmammalian vertebrates.For a long time it was assumed that the human retina contains only two types of photoreceptor cells: the rods and cones responsible for dim-light and daylight vision, respectively. However, recent studies have revealed the existence of a small number of intrinsically photosensitive retinal ganglion cells (ipRGCs) that regulate nonvisual photoresponses (1). ipRGCs express an atypical opsin-like protein named melanopsin (2, 3) which plays a role in the regulation of unconscious visual reflexes and in the synchronization of endogenous physiological responses to the dawn/dusk cycle (circadian rhythms) (4, 5).Melanopsins are unique among vertebrate photoreceptors because their amino acid sequence shares greater similarity to invertebrate than vertebrate rhodopsin (i.e., the photoreceptor of rods) (6, 7). Like rhodopsins, melanopsins feature an up–down bundle architecture of seven transmembrane α-helices incorporating the 11-cis isomer of retinal as a covalently bound protonated Schiff base (PSB11 in Fig. 1A). Light-induced (i.e., photochemical) isomerization of PSB11 to its all-trans isomer (PSBAT) triggers an opsin conformational change that, ultimately, activates the receptor and signaling cascade (8, 9). However, similar to invertebrate and in contrast to vertebrate rhodopsins, melanopsins are bistable (10). Indeed, although vertebrate rhodopsins need a retinoid cycle (11) to regenerate PSB11, melanopsins have an intrinsic light-driven chromophore regeneration function via PSBAT back-isomerization. Furthermore, past studies have shown that melanopsins use an invertebrate-like signal transduction cascade (12).Open in a separate windowFig. 1.PSB11 chromophore reactivity. (A) Chromophore structure and isomerization to PSBAT. (B) Schematic representation of the photochemical (full arrows) and thermal (dashed arrows) isomerization paths. The CI is located energetically above the TS, features a different geometrical structure, and drives a far-from-equilibrium process. ΔE_S1-S0, τ_cis→trans, and Ea^T (in red) are the fundamental quantities computed in the present work.Melanopsins are held responsible for photoentrainment, using the changes of irradiance and spectral composition to adjust the circadian rhythm (13). The different studies carried out so far on melanopsin light sensitivity do not lead to consistent results. Although Do et al. (14) argue that ipRGCs work at extremely low irradiation intensities showing a single-photon response larger than rods, Ferrer et al. (15) conclude that the melanopsin has a reduced sensitivity relative to visual pigments. On the other hand, these photoreceptors would be expected to display high light sensitivity (14). In the vertebrate retina their density is 10⁴ times lower than that of rhodopsins. Moreover, the receptor is not confined in a dedicated cellular domain such as the outer segment of rods and cones, resulting in a ipRGCs photon capture more than 10⁶-fold lower than that of rods and cones per unit of retina illumination. A high sensitivity of melanopsins would also be consistent with their presence in extraretina locations such as in pineal complex, deep brain, and derma of nonmammalian vertebrates (e.g., amphibian) (16–18). The amount of light that can penetrate into such regions is limited and enriched in the red component due to light scattering by the surrounding tissues (14).The molecular-level understanding of the primary light response of melanopsin is a prerequisite for the comprehension of more complex properties such as its activation and sensitivity. Despite numerous studies carried out since its discovery (16), there is presently little information on the molecular mechanism of melanopsin activation. The common PSB11 chromophore of melanopsins and rhodopsins does not guarantee that the same mechanism operates in both photoreceptors. This not only concerns light-induced activation but also thermal activation: a process whose rate limits the photoreceptor light sensitivity and that is currently associated with thermal, rather than photochemical, PSB11 isomerization (19–24).The mechanism of light-induced PSB11 isomerization in vertebrate rhodopsins has been extensively investigated. Spectroscopic studies have shown that in bovine rhodopsin (Rh) the isomerization occurs on a subpicosecond timescale (25–27). Moreover, the observation of ground state (S₀) vibrational coherence (28) is consistent with a direct transfer of the excited state (S₁) population to the photoproduct (Fig. 1B) passing through a conical intersection (CI). Such a path has been located along the S₁ potential energy surface by constructing a multiconfigurational quantum chemistry (MCQC) based computer model of the photoreceptor (29–31) and spectroscopically supported by probing in the infrared (31). More recently (32), the same computer model has been used to map the Rh thermal isomerization path (Fig. 1B) providing information on the transition states controlling the reaction.Here we present a computational study focusing on the mechanism of photochemical and thermal isomerization of human melanopsin (hMeOp). This would require the construction of a computer model of hMeOp starting from the receptor crystal structure. However, the lack of hMeOp crystallographic data does not allow the use of the protocol previously applied in Rh studies. The significant sequence similarity between squid rhodopsin (sqRh), whose crystal structure is available (PDB code: 2Z73) (33), and hMeOp (40%, SI Appendix, Fig. S1) provides the fundamentals for constructing a structural model of hMeOp at a significant atomic resolution. Building on a study by Batista and coworkers (34) on murine melanopsin, we combine comparative modeling of hMeOp with MCQC to construct a quantum mechanics/molecular mechanics (QM/MM) computer model capable of simulating the photochemical and thermal isomerization reactions of hMeOp. The results are then compared with those found using Rh and sqRh models constructed using the same protocol. Such a comparison is expected to provide information on the differences in spectral and functional properties of these evolutionary distant pigments. As we will show below, the models indicate that hMeOp has a faster photochemical isomerization dynamics and a higher thermal isomerization barrier than both Rh and sqRh.     

Mossy fiber-evoked subthreshold responses induce timing-dependent plasticity at hippocampal CA3 recurrent synapses

Dentate granule cells exhibit exceptionally low levels of activity and rarely elicit action potentials in targeted CA3 pyramidal cells. It is thus unclear how such weak input from the granule cells sustains adequate levels of synaptic plasticity in the targeted CA3 network. We report that subthreshold potentials evoked by mossy fibers are sufficient to induce synaptic plasticity between CA3 pyramidal cells, thereby complementing the sparse action potential discharge. Repetitive pairing of a CA3–CA3 recurrent synaptic response with a subsequent subthreshold mossy fiber response induced long-term potentiation at CA3 recurrent synapses in rat hippocampus in vitro. Reversing the timing of the inputs induced long-term depression. The underlying mechanism depends on a passively conducted giant excitatory postsynaptic potential evoked by a mossy fiber that enhances NMDA receptor-mediated current at active CA3 recurrent synapses by relieving magnesium block. The resulting NMDA spike generates a supralinear depolarization that contributes to synaptic plasticity in hippocampal neuronal ensembles implicated in memory.The CA3 area of the hippocampus exhibits a distinctive, highly recurrent circuitry proposed to support autoassociative memory representation (1, 2). This prediction has been confirmed by experimental work demonstrating the pattern completion capabilities of CA3 networks (3), as well as their roles in the spatial tuning of CA1 pyramidal cells, in one-trial contextual learning (4) and in certain forms of memory consolidation (5). CA3 pyramidal cells receive, via the mossy fibers, information processed by granule cells important for both pattern separation (6, 7) and pattern completion functions (7). The faithful transmission of mossy fiber input appears to be ensured by giant synapses composed of presynaptic boutons with up to 45 release sites (8) that target massive spines, the thorny excrescences, on the apical dendrite of CA3 pyramidal cells. Thus, the mossy fiber synapse is often referred to as a detonator synapse (9). In fact, mossy fiber signaling is more compatible with a gatekeeper function than a high-throughput data relay. Although high-frequency bursts of action potentials in a hippocampal granule cell can discharge a targeted CA3 pyramidal cell, the majority of responses evoked by granule cells in CA3 pyramidal cells do not attain the firing threshold (10). Nevertheless, mossy fibers generate powerful signals evoking subthreshold responses that are much larger than typical synaptic events in the brain, with excitatory postsynaptic potentials (EPSPs) and excitatory postsynaptic currents (EPSCs) reaching amplitudes of 10 mV and 1 nA, respectively (11). Here we examined in rat slice cultures how EPSPs generated at mossy fiber synapses are processed in CA3 pyramidal cell dendrites, and evaluated whether subthreshold synaptic responses evoked by mossy fiber stimulation can act as instructive signals to induce plasticity at the pyramidal cell synapses forming the CA3 recurrent network.     

Incisional hernia after laparoscopic colorectal surgery. Is there any factor associated?

Background

Laparoscopic approach is related to, among others, educing abdominal wall complications such as incisional hernia (IH). However, there are scarce data concerning laparoscopic colorectal surgery (LCRS). The aim of this study was to evaluate related factors and incidence of IH following this approach.

Methods

A retrospective analysis of consecutive patients who underwent colorectal surgery with laparoscopic approach in a single center was performed. Patients with a minimum follow-up of 6 months, and also converted to open surgery were included. Uni- and multi-variate analyses were performed using the following variables: age; gender; type of surgery (left, right, total, or segmental colectomy); comorbidities [diabetes and chronic pulmonary obstructive disease (COPD)]; previous surgery; colorectal disease (benign and malignant); operative time; surgical site infection (SSI); and body mass index (BMI). Midline incisions (right colectomy) and off-midline incisions (left colectomies and rectal resections) were also compared.

Results

During a period of 12 years, 1051 laparoscopic colorectal surgeries were performed. The incidence of IH was 6 % (n = 63). Univariate analysis showed that BMI > 30 kg/m² [p < 0.01, OR: 2.3 (1.3–4.7)], SSI [p < 0.01, OR: 6.5 (3.4–12.5)], operative time >180 min [p < 0.01, OR: 2.1 (1.2–3.6)] and conversion to open surgery (p = 0.01, OR: 2.4 [1.1–5.0]) were related to incisional hernias. BMI and SSI have a statistically significant relation with the incidence of IH in multivariate analysis (p < 0.01). No statistical difference between right and left colectomy was observed (6.6 vs. 6.4 %, respectively).

Conclusion

The incidence of IH after LCRS seems to be acceptable. BMI over 30 kg/m² and SSI are strongly associated to this complication.     

Schloffer's tumor: Case report and review of the literature

INTRODUCTION

The so-called Schloffer tumor (ST) is a rare inflammatory pseudotumor. It usually appears several years after abdominal surgery or trauma.

PRESENTATION OF CASE

A 32-year-old man was referred to our hospital complaining of a painful mass in the left hypochondrium, postprandial distension and a weight loss of about 14 kg. He had had a left inguinal hernioplasty without mesh the previous year. Ultrasonography of the abdomen showed a 2 cm × 2 cm hypoechoic lesion in contact with the abdominal wall. Computerized tomography of the abdomen showed a heterogeneous mass in the great omentum.Laparoscopic exploration revealed an omental mass firmly attached to the abdominal wall. A great deal of purulent fluid spread during the procedure. Due to the difficult exploration, the procedure converted to hand assisted laparoscopy. We find an omental tumor involving the stomach and the transverse colon. Inside the mass there were purulent material and non-absorbable sutures. A drain was left inside the cavity of the abscess. Histological examination showed chronic inflammation.

DISCUSSION

ST characteristically presents a central chronic abscess containing non-absorbable sutures. It has been described after appendectomy, hernioplasty, hysterectomy, gastrectomy or colonic resections. Although benign, its progressive growth and infiltrating behavior resemble malignant tumors.

CONCLUSION

We suggest that a mini-invasive approach should always be performed. The interesting thing about this case is the appearance of the tumor in a place far away from the previous surgical site. A simple drainage and removal of suture material solves the problem of these patients.     

Comparison of first trimester, second trimester and integrated Down's syndrome screening results in unaffected pregnancies.

Our aim was to compare the results of first trimester combined test, second trimester triple test, and integrated test in the same pregnant population. We retrospectively studied 927 women, all giving birth to an unaffected baby except for two cases of Down's syndrome. The women underwent a nuchal translucency ultrasound measurement and a blood sampling for pregnancy-associated plasma protein A and free beta-hCG subunit (free total chorionic gonadotropin subunit) assay in the first trimester of pregnancy. A second trimester biochemical screening (alpha-fetoprotein, unconjugated oestriol and total hCG) was performed later. The correlations between each pair of markers and between each marker level and maternal age were calculated. No marker showed significant correlation with any other or with maternal age, with the obvious exception of free beta-hCG subunit and total hCG. The false-positive rate (cut-off level: 1 in 350 at term) was 1.5% for the first trimester test, 3.6% for the second trimester test and 0.54% for the integrated test. In 10/14 pregnancies, the increased risk in the first trimester was not confirmed neither in the second trimester nor by the integrated test. In 29/33 women with an increased risk in the second trimester, the first trimester and the integrated test results were discordant. The absence of correlation among different marker levels suggests that the information supplied by the first and second trimester tests is different. Integrating first and second trimester markers in a single test could pose the ethical problem of withholding first trimester results and thus denying the possible advantages of an earlier pregnancy termination.     

Perioperative and Oncologic Outcomes of Nephrectomy and Caval Thrombectomy Using Extracorporeal Circulation and Deep Hypothermic Circulatory Arrest for Renal Cell Carcinoma Invading the Supradiaphragmatic Inferior Vena Cava and/or Right Atrium

Background

Radical nephrectomy (RN) and caval thrombectomy (CT) for renal cell carcinoma, with extracorporeal circulation (ECC) and deep hypothermic circulatory arrest (DHCA) is a challenging surgical approach.

Management of Appendicitis Globally Based on Income of Countries (MAGIC) Study

Background

Our aim is to compare the management approaches and clinical outcomes of acute appendicitis according to annual Gross National Income per Capita (GNI/Capita) of countries.

Methods

Consecutive patients who were diagnosed to have acute appendicitis from 116 centers of 44 countries were prospectively studied over a 6-month period (April–September 2016). Studied variables included demography, Alvarado score, comorbidities, radiological and surgical management, histopathology, and clinical outcome. Data were divided into three groups depending on the GNI/Capita.

Results

A total of 4271 patients having a mean (SD) age of 33.4 (17.3) years were studied. Fifty-five percent were males. Two hundred and eighty patients were from lower–middle-income (LMI) countries, 1756 were from upper–middle-income (UMI) countries, and 2235 were from high-income (HI) countries. Patients in LMI countries were significantly younger (p?<?0.0001) and included more males (p?<?0.0001). CT scan was done in less than 8% of cases in LMI countries, 23% in UMI countries, and 38% in HI countries. Laparoscopy was performed in 73% of the cases in the HI countries, while open appendectomy was done in more than 60% of cases in both LMI and UMI countries (p?<?0.0001). The longest mean hospital stay was in the UMI group (4.84 days). There was no significant difference in the complication or death rates between the three groups. The overall death rate was 3 per 1000 patients.

Conclusions

There is great variation in the presentation, severity of disease, radiological workup, and surgical management of patients having acute appendicitis that is related to country income. A global effort is needed to address this variation. Individual socioeconomic status could be more important than global country socioeconomic status in predicting clinical outcome.

     

Micro-ureteroscopy vs. ureteroscopy: effects of miniaturization on renal vascularization and intrapelvic pressure

Purpose

Ureteroscopy (URS) is related to complications, as fever or postoperative urinary sepsis, due to high intrapelvic pressure (IPP) during the procedure. Micro-ureteroscopy (m-URS) aims to reduce morbidity by miniaturizing the instrument. The objective of this study is to compare IPP and changes in renal haemodynamics, while performing m-URS vs. conventional URS.

Methods

A porcine model involving 14 female pigs was used in this experimental study. Two surgeons performed 7 URS (8/9.8 Fr), for 45 min, and 7 m-URS (4.85 Fr), for 60 min, representing a total of 28 procedures in 14 animals. A catheter pressure transducer measured IPP every 5 min. Haemodynamic parameters were evaluated by Doppler ultrasound. The volume of irrigation fluid employed in each procedure was also measured.

Results

The range of average pressures was 5.08–14.1 mmHg in the m-URS group and 6.08–20.64 mmHg in the URS (NS). 30 mmHg of IPP were not reached in 90% of renal units examined with m-URS, as compared to 65% of renal units in the URS group. Mean peak diastolic velocity decreased from 15.93 to 15.22 cm/s (NS) in the URS group and from 19.26 to 12.87 cm/s in the m-URS group (p < 0.01). Mean resistive index increased in both groups (p < 0.01). Irrigation fluid volume used was 485 mL in the m-URS group and 1475 mL in the URS group (p < 0.001).

Conclusions

m-URS requires less saline irrigation volumes than the conventional ureteroscopy and increases renal IPP to a lesser extent.