Accuracy of global longitudinal and territorial longitudinal strain in determining myocardial viability in out of window period Anterior wall myocardial infarction patients

Funding Acknowledgements

Type of funding sources: None.

Background

Primary percutaneous intervention remains the principal treatment modality for anterior wall myocardial infarction (AWMI). However, a large fraction of patients especially in the developing countries present outside the window period (OWP) with no chest pain and akinetic left anterior descending (LAD) territory on echocardiography. Revascularization in these patients is primarily guided by viability status.

Purpose

This study was conducted to determine the accuracy of strain echocardiographic parameters compared to single-photon emission computed tomography (SPECT) in predicting myocardial viability in patients of AWMI presenting OWP.

Methods

All patients presenting with AWMI-OWP without ongoing chest pain and akinetic LAD territory on echocardiography from December 2020 to June 2021 were recruited. All patients underwent determination of both Global longitudinal strain (GLS) and territorial longitudinal strain (TLS) within 24-72 hours on AWMI. In addition, all underwent SPECT to determine the percentage of non-viable myocardium. On SPECT, a defect >5% myocardial territory showing severe reperfusion defect was considered as a marker of non-viability. 

Results

A total of 27 patients were recruited. The mean age of the population was 61.66 + 12.6 years. Acute left ventricular failure (LVF) and cardiogenic shock (CS) was present in 6 (22.2%) and 5 (18.5%) patients respectively. Out of 22 patients who underwent angiography, majority of the patients 19 (86%) had single vessel disease involving the LAD.

The mean left ventricular ejection fraction (LVEF) of the study group was 29.6 + 6.5%. The mean GLS and LAD territory TLS of the study group was -11.13 + 3.14% and -7.2 + 2.75% respectively. On SPECT, 8 (29.6%) patients had non-viable underlying myocardium.

Parameters that very significantly associated with non-viability on SPECT included past history of CAD (p = 0.004), smoking (p = 0.05) and presentation with LVF (p = 0.0008) and CS (p = 0.001).

The mean LVEF was significantly lower in the group with non-viability on SPECT (32.3 + 5.1% vs 23.1 + 4.5%; p < 0.001). Both GLS (-12.8 + 1.4% vs -7.1+ 2.3%; p < 0.001) and TLS (-8.7 + 1.4% vs -3.8 + 1.8%; p < 0.001) were significantly lower in group showing non-viability on SPECT.

On receiver operating curves, a GLS of > -10.45% and TLS of > -6.65%, both had a sensitivity of 87.5% and specificity of 89.5% in predicting non-viability on SPECT. Both showed good accuracy in predicting non-viability on overall quality model. (Figures 1 and 2)

Conclusion

Modalities like cardiac magnetic resonance, SPECT or positron emission tomography are resource dependent and take time to be performed. Hence, performing these investigations is challenging in unstable patients. Strain echocardiography provides GLS of the myocardium which has good sensitivity and specificity in predicting viability and can be performed safely and quickly in this high-risk group. Abstract Figure.  Abstract Figure. Overall quality model

Angiographic Profiles in Persistent Non-Valvular Atrial Fibrillation Patients

Funding Acknowledgements

Type of funding sources: None.

OnBehalf

Cardiology dept. PGIMER, Chandigarh

Background

The relationship of atrial fibrillation (AF) with coronary artery disease (CAD) is well established. Atrial ischemia due to obstructive CAD has been identified as one of the key risk factors, leading to AF. However, sufficient evidence exists as to the presence of myocardial ischemia on stress imaging, even without the presence of obstructive CAD in AF patients. Slow flow and coronary tortuosity on angiogram can lead to downstream myocardial ischemia independent of CAD. 

Purpose

We aimed to delineate the angiographic profiles in AF patients with attention to slow flow and tortuosity leading to ischemia in those without obstructive CAD. 

Methods

The study was a nonrandomised, prospective, single-centre observational study of consecutive patients of persistent non valvular AF. Symptomatic patients despite optimal medical therapy (OMT) for 3 months were recruited and all underwent coronary angiograms (CAG). Patients with known CAD or prior history of myocardial infarction were excluded. Further angiographic analysis was done in those without obstructive CAD to determine incidence of slow flow (>27 corrected TIMI frame count) and tortuosity (presence of ≥3 fixed bends in an epicardial artery). 

Results

A total of 70 patients were recruited and followed for a mean duration of 12 ± 1.4 months. The mean age of the study group was 66.07 (±11.49). Hypertension (74%) was the commonest comorbidity followed by obesity (35%) and diabetes (30%). At CAG, 32/70 (46%) had obstructive CAD, 17/70 (24%) had non obstructive (<50-70% stenosis) CAD and 21/70 (30%) had normal coronaries without atherosclerosis. Amongst patients without obstructive CAD (n = 38) slow flow was seen in 16/38 (42%) and coronary tortuosity in 11/38 (29%) patients. There ware no differences in terms of death, HF and FVR hospitalisations or stroke at follow up between the obstructive CAD vs no obstructive CAD. However in patients without obstructive CAD, hospitalisations for FVR was significantly increased in those having slow flow on CAG, 9/12 (75%) vs 7/26 (27%) in those without slow flow (p value = 0.005). The mean TIMI frame count was also significantly higher in those with FVR hospitalisations 35.3 ± 11 vs 25.8 ± 8.9  (p value = 0.005). TIMI frame count >31 had a sensitivity of 83% and a specificity of 69% for predicting hospitalisations for FVR on ROC curve(AUC = 0.71). 

Conclusions

CAD is closely related to AF and majority (70%) of our patients had evidence of atherosclerotic CAD on CAG in our study. A large proportion of patients with no evidence of obstructive CAD on CAG had slow flow or coronary tortuosity. Significantly increased hospitalisation for FVR seen in the slow flow group shows its significance and may lead to newer treatment modalities in future. Further larger studies looking at these aspects on CAG may give further insight as to the nature and prognosis of these entities. Abstract Figure 1: Flow diagram showing the patie

Observational study of Covid-19 patients presenting with acute coronary syndrome at a tertiary care center in India

Aim

Patients with Covid-19 are theoretically at a higher risk of ACS, as respiratory infections can often lead to coronary endothelial damage and plaque rupture. Initial reports during start of pandemic suggested decrease in STEMI patients, however this has been explained by iatrophobia rather than actual decrease. Data on pathophysiology and outcome of patients presenting with ACS is scarce. We did a prospective observational study to study epidemiology and outcomes of Covid-19 patients with ACS.

Methods

A total of 654 patients were admitted with Covid-19 at PGIMER, Chandigarh from August 2020 to February 2021, 35 (5.3%) consecutive patients of ACS were enrolled into the study. Acute myocardial infarction was defined as per fourth universal definition of myocardial infarction. Diagnosis of Covid-19 was established using RT-PCR from nasopharyngeal swab. Angiographic assessment was done by two interventional cardiologists.

Results

Mean age of patients was 59.5±11.8 years, males comprised majority (80%) of study group. Most common risk factor was hypertension seen in around 70% followed by DM in 57% patients. Most common symptom at presentation was rest angina seen >90% while history of fever was present in only 31.4%. STEMI was most common ACS seen in 45.7% followed by USA in 23% patients. CS was present in 15% patients at presentation while another 5% developed shock in hospital. Oxygen requirement was required in over half the patients while 25% patients succumbed to illness in hospital.Thrombolysis was done in half the patients of STEMI. In view of Covid-19 disease 71.4% required dexamethasone and remdesivir. Coronary angiography was done in around 20% patients, which revealed obstructive CAD in 83% patients with 60% patients having 100% occlusion of IRA. Percutaneous intervention was done in 66% patients. Hypoalbuminemia was commonly seen patients with mean albumin of 3.3 gm/dL. Low T3 syndrome was most common thyroid function abnormality seen in 37.1%.On univariate analysis age, BNP levels and albumin were able to predict 30-day mortality.

Conclusion

ACS can be first presentation of patients with Covid-19 as shown by our study only 30% patients had prior history of fever. Our data reaffirms that patients with Covid-19 and ACS have worse prognosis. Interestingly mortality in our study was comparable to western study, despite low rate of angiography and intervention thus underscoring individualization of therapy. We believe Type-2 myocardial infarction is common in pathophysiology of patients who benefit most from medical therapy.

Funding Acknowledgement

Type of funding sources: None.

Angiographic profiles in patients of persistent non-valvular atrial fibrillation from a tertiary care center in north india

Funding Acknowledgements

Type of funding sources: None.

Background

The relationship of atrial fibrillation (AF) with coronary artery disease (CAD) is well established. Atrial ischemia due to obstructive CAD has been identified as one of the key risk factors, leading to AF. However, sufficient evidence exists as to the presence of myocardial ischemia on stress imaging, even without the presence of obstructive CAD in AF patients. Slow flow and coronary tortuosity on angiogram can lead to downstream myocardial ischemia independent of CAD.

Purpose

We aimed to delineate the angiographic profiles in AF patients with attention to slow flow and tortuosity leading to ischemia in those without obstructive CAD.

Methods

The study was a nonrandomised, prospective, single-centre observational study of consecutive patients of persistent non valvular AF. Symptomatic patients despite optimal medical therapy (OMT) for 3 months were recruited and all underwent coronary angiograms (CAG). Patients with known CAD or prior history of myocardial infarction were excluded. Further angiographic analysis was done in those without obstructive CAD to determine incidence of slow flow (>27 corrected TIMI frame count) and tortuosity (presence of ≥3 fixed bends in an epicardial artery).

Results

A total of 70 patients were recruited and followed for a mean duration of 12 ± 1.4 months. The mean age of the study group was 66.07 (±11.49). Hypertension (74%) was the commonest comorbidity followed by obesity (35%) and diabetes (30%). At CAG, 32/70 (45%) had obstructive CAD, 17/70 (24%) had non obstructive (<50-70% stenosis) CAD and 21/70 (30%) had normal coronaries without atherosclerosis. Amongst patients without obstructive CAD (n = 38) slow flow was seen in 16/38 (42%) and coronary tortuosity in 11/38 (29%) patients. There ware no differences in terms of death, HF and FVR hospitalisations or stroke at follow up between the obstructive CAD vs no obstructive CAD. However in patients without obstructive CAD, hospitalisations for FVR was significantly increased in those having slow flow on CAG, 9/12 (75%) vs 7/26 (27%) in those without slow flow (p value = 0.005). The mean TIMI frame count was also significantly higher in those with FVR hospitalisations 35.3 ± 11 vs 25.8 ± 8.9  (p value = 0.005). TIMI frame count >31 had a sensitivity of 83% and a specificity of 69% for predicting hospitalisations for FVR on ROC curve(AUC = 0.71).

Conclusions

CAD is closely related to AF and majority (70%) of our patients had evidence of atherosclerotic CAD on CAG in our study. A large proportion of patients with no evidence of obstructive CAD on CAG had slow flow or coronary tortuosity. Significantly increased hospitalisation for FVR seen in the slow flow group shows its significance and may lead to newer treatment modalities in future. Further larger studies looking at these aspects on CAG may give further insight as to the nature and prognosis of these entities.

A Blind, Numerical Benchmark Study on Supercritical Water Heat Transfer Experiments in a 7-Rod Bundle

Heat transfer in supercritical water reactors (SCWRs) shows a complex behavior, especially when the temperatures of the water are near the pseudocritical value. For example, a significant deterioration of heat transfer may occur, resulting in unacceptably high cladding temperatures. The underlying physics and thermodynamics behind this behavior are not well understood yet. To assist the worldwide development in SCWRs, it is therefore of paramount importance to assess the limits and capabilities of currently available models, despite the fact that most of these models were not meant to describe supercritical heat transfer (SCHT). For this reason, the Gen-IV International Forum initiated the present blind, numerical benchmark, primarily aiming to show the predictive ability of currently available models when applied to a real-life application with flow conditions that resemble those of an SCWR. This paper describes the outcomes of ten independent numerical investigations and their comparison with wall temperatures measured at different positions in a 7-rod bundle with spacer grids in a supercritical water test facility at JAEA. The wall temperatures were not known beforehand to guarantee the blindness of the study. A number of models have been used, ranging from a one-dimensional (1-D) analytical approach with heat transfer correlations to a RANS simulation with the SST turbulence model on a mesh consisting of 62 million cells. None of the numerical simulations accurately predicted the wall temperature for the test case in which deterioration of heat transfer occurred. Furthermore, the predictive capabilities of the subchannel analysis were found to be comparable to those of more laborious approaches. It has been concluded that predictions of SCHT in rod bundles with the help of currently available numerical tools and models should be treated with caution.

Turbulent Heat Transfer to Heavy Liquid Metals in Circular Tubes

The present paper gives a brief literature review on turbulent heat transfer in heavy liquid metals (HLM), especially liquid lead-bismuth eutectic (LBE). Some models available in the open literature on heat transfer and turbulent Prandtl number are assessed. In addition, CFD analysis is carried out for circular tube geometries. The effect of turbulence models, mesh structure and turbulent Prandtl number on the numerical results is studied. Application of ε-type turbulence models with scalable wall function shows less dependence of the numerical results on mesh structure than the ω-type turbulence models with automatic wall treatment. The turbulent Prandtl number affects strongly the heat transfer performance. Comparison between the CFD results, heat transfer correlations and heat transfer test data reveals a decrease in turbulent Prandtl number by increasing Reynolds number. Based on the results achieved, recommendations are made on correlations of heat transfer and turbulent Prandtl number for LBE flows.

Developmental sensitivity of associative learning to cholesterol synthesis inhibitors

Patients with Smith-Lemli-Opitz syndrome, a genetic disorder associated with severe mental retardation, are unable to convert 7-dehydrocholesterol to cholesterol. Treatment of rats with agents that block cholesterol synthesis produces a sterol profile reminiscent of Smith-Lemli-Opitz patients i.e., low levels of cholesterol accompanied by the appearance of its immediate precursor 7-dehydrocholesterol. In previous work, chronic inhibition of cholesterol synthesis in just-weaned rats impaired acquisition of the classically conditioned eyeblink response. The present study had two primary goals--(1) to determine whether the learning impairment depended on the age in which treatment was initiated; and (2) to determine whether the deficit was associative or due to performance factors. Consistent with earlier work, acquisition of the eyeblink conditioned response was impaired when the 30-day treatment was initiated on postnatal day (PND) 21. Reactivity to acoustic stimuli and to eyelid stimulation were normal, suggesting that the learning impairment was associative in nature. The learning impairment was transitory; acquisition was normal when evaluated 30 days after the cessation of treatment. When treatment was initiated 30 days after weaning (PND 51), acquisition of the eyeblink response was normal. However, brain sterols of young adult rats were less affected than those of just-weaned rats. Thus, there is a developmental sensitivity to cholesterol synthesis blocking agents both in terms of their effects on brain sterols and new motor learning.

Cholecystectomy prevents expansion of the bile acid pool and inhibition of cholesterol 7alpha-hydroxylase in rabbits fed cholesterol

To study the effect of cholecystectomy on the regulation of classic and alternative bile acid syntheses, gallbladder-intact (n = 20) and cholecystectomized (n = 20) New Zealand White rabbits were fed either chow or chow with 2% cholesterol (3 g/day). After 10 days, bile fistulas were constructed in half of each rabbit group to recover and measure the bile acid pool and biliary bile acid flux. After cholesterol feeding, the bile acid pool size increased from 268 +/- 55 to 444 +/- 77 mg (P < 0.01) with a 2-fold rise in the biliary bile acid flux in intact rabbits but did not expand the bile acid pool (270 +/- 77 vs. 276 +/- 62 mg), nor did the biliary bile acid flux increase in cholecystectomized rabbits. Ileal apical sodium-dependent bile acid transporter protein increased 46% from 93 +/- 6 to 136 +/- 23 units/mg (P < 0.01) in the intact rabbits but did not change in cholecystectomized rabbits (104 +/- 14 vs. 99 +/- 19 units/mg) after cholesterol feeding. Cholesterol 7alpha-hydroxylase activity was inhibited 59% (P < 0.001) while cholesterol 27-hydroxylase activity rose 83% (P < 0.05) after cholesterol feeding in the intact rabbits but neither enzyme activity changed significantly in cholesterol-fed cholecystectomized rabbits. Fecal bile acid outputs reflecting bile acid synthesis increased significantly in the intact but not in the cholecystectomized rabbits fed cholesterol. Removal of the gallbladder prevented expansion of the bile acid pool after cholesterol feeding as seen in intact rabbits because ileal bile acid transport did not increase. As a result, cholesterol 7alpha-hydroxylase was not inhibited.

The effect of the erg26-1 mutation on the regulation of lipid metabolism in Saccharomyces cerevisiae

A temperature-sensitive Saccharomyces cerevisiae mutant harboring a lesion in the ERG26 gene has been isolated. ERG26 encodes 4alpha-carboxysterol-C3 dehydrogenase, one of three enzymatic activities required for the conversion of 4,4-dimethylzymosterol to zymosterol. Gas chromatography/mass spectrometry analyses of sterols in this mutant, designated erg26-1, revealed the aberrant accumulation of a 4-methyl-4-carboxy zymosterol intermediate, as well as a novel 4-carboxysterol. Neutral lipid radiolabeling studies showed that erg26-1 cells also harbored defects in the rate of biosynthesis and steady-state levels of mono-, di-, and triglycerides. Phospholipid radiolabeling studies showed defects in the rate of biosynthesis of both phosphatidic acid and phosphatidylinositol. Biochemical studies revealed that microsomes isolated from erg26-1 cells contained greatly reduced 4alpha-carboxysterol-C3 dehydrogenase activity when compared with microsomes from wild type cells. Previous studies have shown that loss of function mutations in either of the fatty acid elongase genes SUR4/ELO3 or FEN1/GNS1/ELO2 can "bypass" the essentiality of certain ERG genes (Ladeveze, V., Marcireau, C., Delourme, D., and Karst, F. (1993) Lipids 28, 907-912; Silve, S., Leplatois, P., Josse, A., Dupuy, P. H., Lanau, C., Kaghad, M., Dhers, C., Picard, C., Rahier, A., Taton, M., Le Fur, G., Caput, D., Ferrara, P., and Loison, G. (1996) Mol. Cell. Biol. 16, 2719-2727). Studies presented here have shown that this sphingolipid-dependent "bypass" mechanism did not suppress the essential requirement for zymosterol biosynthesis. However, studies aimed at understanding the underlying physiology behind the temperature-sensitive growth defect of erg26-1 cells showed that the addition of several antifungal compounds to the growth media of erg26-1 cells could suppress the temperature-sensitive growth defect. Fluorescence microscopic analysis showed that GFP-Erg26p and GFP-Erg27p fusion proteins were localized to the endoplasmic reticulum. Two-hybrid analysis indicated that Erg25p, Erg26p, and Erg27p, which are required for the biosynthesis of zymosterol, form a complex within the cell.

Comparative regulation of hepatic sterol 27-hydroxylase and cholesterol 7alpha-hydroxylase activities in the rat, guinea pig, and rabbit: effects of cholesterol and bile acids

The regulation of the classic and alternative bile acid synthetic pathways by key hepatic enzyme activities (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase, respectively) was examined in bile acid depletion and replacement and cholesterol-feeding experiments with rats, guinea pigs, and rabbits. The bile acid pool was depleted by creating a bile fistula (BF) and collecting bile for 2 to 5 days, and it was replaced by intraduodenal infusion of the major biliary bile acids (taurocholic acid [TCA], glycochenodeoxycholic acid [GCDCA], and glycocholic acid [GCA] in the rat, guinea pig, and rabbit, respectively) at rates equivalent to the measured hepatic flux of the bile acids. To study the effects of cholesterol, the animals were fed for 7 days on a basal diet with and without 2% cholesterol. Cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities, measured by isotope incorporation assays, were related to bile acid output and composition and hepatic cholesterol concentrations. Intraduodenal infusion of bile acids increased the output of the tested bile acids, but did not significantly change hepatic cholesterol concentrations and had no effect on sterol 27-hydroxylase activity. Neither bile acid depletion nor replacement affected sterol 27-hydroxylase activity when three different substrates (cholesterol, 5beta-cholestane-3alpha,7alpha-diol, and 5beta-cholestane-3alpha,7alpha,12alpha-triol) were tested. In contrast, feeding 2% cholesterol increased hepatic cholesterol concentrations in rats, guinea pigs, and rabbits threefold, twofold, and eightfold, respectively, and increased hepatic mitochondrial sterol 27-hydroxylase activity (conversion of cholesterol to 27-hydroxycholesterol) in all three animal models. The stimulation and feedback inhibition of cholesterol 7alpha-hydroxylase activity by bile acid depletion and replacement were observed in all three animal models, whereas the effect of cholesterol feeding was species-dependent (cholesterol 7alpha-hydroxylase activity increased in the rat, did not change in the guinea pig, and was inhibited in the rabbit). Thus, in contrast to sterol 27-hydroxylase, which was upregulated by cholesterol but not affected by bile acid depletion and replacement in all three animal models, cholesterol 7alpha-hydroxylase activity was controlled consistently and inversely by the hepatic flux of bile acids, but was species-dependent in its response to a 1-week feeding with 2% cholesterol.

Rapid identification of Smith-Lemli-Opitz syndrome homozygotes and heterozygotes (carriers) by measurement of deficient 7-dehydrocholesterol-delta 7-reductase activity in fibroblasts

To extend the enzyme deficiency in Smith-Lemli-Opitz syndrome (SLOS) to extrahepatic tissues, 7-dehydrocholesterol-delta 7-reductase activity was measured in fibroblasts from 10 controls, five SLOS homozygotes, and five obligate heterozygotes. In cells grown almost to confluence in cholesterol-containing medium (4 mg/dL), the conversion of [1,2-3H]7-dehydrocholesterol to cholesterol (7-dehydrocholesterol-delta 7-reductase activity) was 3.8 times higher in control than in homozygote cells and 2.2 times higher than in heterozygote cells. After 24 hours' exposure of the fibroblasts to cholesterol-deficient medium supplemented with lovastatin, 7-dehydrocholesterol-delta 7-reductase activity increased twofold in controls, but did not change significantly in either heterozygous or homozygous cells. In contrast, the activities of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and lathosterol 5-dehydrogenase, two key enzymes that precede 7-dehydrocholesterol-delta 7-reductase in the cholesterol biosynthetic pathway, and low-density lipoprotein (LDL) receptor-mediated binding were equal in control, homozygote, and heterozygote fibroblasts. Further, HMG-CoA reductase activity and LDL receptor-mediated binding increased after exposure of the cells to cholesterol-deficient medium. Fibroblast cholesterol concentrations were approximately equal, although homozygote cells contained 30 times more 7-dehydrocholesterol. Thus, markedly reduced 7-dehydrocholesterol-delta 7-reductase activity that cannot be upregulated after exposure of the cells to cholesterol-deficient medium is diagnostic for the biochemical defect in SLOS. Significantly reduced enzyme activity between the levels in controls and homozygotes without accumulation of 7-dehydrocholesterol in fibroblasts identified heterozygotes.

Regulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in the rat ileum: effects of bile acids and lovastatin

We investigated the effects of intestinal bile acid flux, orientation of the 7-hydroxy group, and administration of lovastatin on the regulation of intestinal 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase activity in the rat ileum. HMG-CoA reductase activities in villous and crypt cells from the ileal mucosa were similar, and the study was performed on whole mucosa that contained both cell types. Taurocholate feeding decreased ileal reductase activity 48%, whereas tauroursocholate, the 7 beta-hydroxy epimer of taurocholate, had no effect. Feeding lovastatin (inhibitor of HMG-CoA reductase) stimulated total ileal HMG-CoA reductase activity threefold in washed microsomes, which were dissociated from the inhibitor. However, the proportion of active enzyme in the ileum of lovastatin-fed rats was 50% lower than in controls, whereas there was no change in the percentage of expressed enzyme with bile acid treatments. Interruption of the enterohepatic circulation (bile fistula) increased HMG-CoA reductase activity in the ileum 73%. Duodenal infusion of taurocholate to bile-fistula rats significantly decreased microsomal HMG-CoA reductase activity in the ileal mucosa. In contrast, infusion of the 7 beta-hydroxy epimer tauroursocholate failed to inhibit the derepressed HMG-CoA reductase activity in the ileum of bile-fistula rats. The inhibition of intestinal HMG-CoA reductase activity by taurocholate occurred without accumulation of mucosal cholesterol. Furthermore, the stimulation of total ileal HMG-CoA reductase activity by lovastatin treatment was observed without a decrease in mucosal cholesterol. In summary, the regulation of ileal HMG-CoA reductase activity by the intestinal luminal flux of bile acids is dependent on the orientation of the hydroxyl groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of cholesterol 7 alpha-hydroxylase from human and rat liver and production of inhibiting polyclonal antibodies

Cholesterol 7 alpha-hydroxylase, the cytochrome P-450-dependent and rate-controlling enzyme of bile acid synthesis, was purified from rat and human liver microsomes. The purified fractions were assayed in a reconstituted system containing [4-14C]cholesterol, and cholesterol 7 alpha-hydroxylase activities in these fractions increased 500-600-fold relative to whole microsomes. Polyacrylamide gel electrophoresis of rat microsomes followed by immunoblotting with polyclonal rabbit antisera raised against purified cholesterol 7 alpha-hydroxylases revealed two peaks at molecular masses of 47,000 and 49,000 daltons for both rat and human fractions. Increasing amounts of rabbit anti-rat and anti-human antibodies progressively inhibited rat microsomal cholesterol 7 alpha-hydroxylase activity up to 80%. In contrast, monospecific antibodies raised against other purified cytochrome P-450 enzymes (P-450f, P-450g, and P-450j) did not inhibit rat or human cholesterol 7 alpha-hydroxylase activity. Immunoblots of rat microsomes with the rabbit anti-rat cholesterol 7 alpha-hydroxylase antibody demonstrated that the antibody reacted quantitatively with the rat microsomal enzyme. Microsomes from cholesterol-fed rats showed increased cholesterol 7 alpha-hydroxylase mass, whereas treatment with pravastatin, an inhibitor of hydroxy-methylglutaryl-coenzyme A reductase, reduced enzyme mass. Microsomes from starved rats contained slightly less cholesterol 7 alpha-hydroxylase protein than chow-fed control rats. These results indicate a similarity in molecular mass, structure, and antigenicity between rat and human cholesterol 7 alpha-hydroxylases; demonstrate the production of inhibiting anti-cholesterol 7 alpha-hydroxylase antibodies that can be used to measure the change in cholesterol 7 alpha-hydroxylase enzyme mass under various conditions; and emphasize the unique structure of cholesterol 7 alpha-hydroxylase with respect to other cytochrome P-450-dependent hydroxylases.