Chimeric antigen receptor (CAR) T-cell therapy for people with relapsed or refractory diffuse large B-cell lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) is an aggressive cancer of the lymphatic system. About 30% to 40% of people with DLBCL experience relapse and 10% are refractory to first-line treatment usually consisting of R-CHOP chemotherapy. Of those eligible for second-line treatment, commonly consisting of salvage chemotherapy followed by autologous stem-cell transplantation (ASCT), around 50% experience relapse. With a median overall survival of less than six to 12 months, the prognosis of individuals who relapse or are refractory (r/r) to advanced lines of treatment or of those who are ineligible for ASCT, is very poor. With the introduction of chimeric antigen receptor (CAR) T-cell therapy, a novel treatment option for these people is available.

OBJECTIVES

To assess the benefits and harms of chimeric antigen receptor (CAR) T-cell therapy for people with relapsed or refractory (r/r) DLBCL.

SEARCH METHODS

An experienced information specialist performed a systematic database search for relevant articles on CENTRAL, MEDLINE and Embase until September 11th, 2020. We also searched trial registries and reference lists of identified studies up to this date. All search results were screened by two authors independently and a third author was involved in case of discrepancies.

SELECTION CRITERIA

We included prospectively planned trials evaluating CAR T-cell therapy for people with r/r DLBCL. We had planned to include randomised controlled trials (RCTs) and we flexibly adapted eligibility criteria to the most reliable study designs available. We excluded studies involving fewer than 10 participants with r/r DLBCL and studies with a proportion of participants with r/r DLBCL below 70%, unless data were reported separately for this subgroup.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data and performed risk of bias ratings independently. A third author was involved in case of disagreements. As our search did not yield any completed RCTs, prospective controlled non-randomised studies of interventions (NRSIs) or prospective observational studies with a control group, we did not meta-analyse data and reported all results narratively. We adopted the GRADE approach to assess the certainty of the evidence for prioritised outcomes.

MAIN RESULTS

We identified 13 eligible uncontrolled studies evaluating a single or multiple arms of CAR T-cell therapies. We also identified 38 ongoing studies, including three RCTs. Ten studies are awaiting classification due to completion with no retrievable results data or insufficient data to justify inclusion. The mean number of participants enrolled, treated with CAR T-cell therapy and evaluated in the included studies were 79 (range 12 to 344; data unavailable for two studies), 61 (range 12 to 294; data unavailable for one study) and 52 (range 11 to 256), respectively. Most studies included people with r/r DLBCL among people with other haematological B-cell malignancies. Participants had received at least a median of three prior treatment lines (data unavailable for four studies), 5% to 50% had undergone ASCT (data unavailable for five studies) and, except for two studies, 3% to 18% had undergone allogenic stem-cell transplantation (data unavailable for eight studies). The overall risk of bias was high for all studies, in particular, due to incomplete follow-up and the absence of blinding. None of the included studies had a control group so that no adequate comparative effect measures could be calculated. The duration of follow-up varied substantially between studies, in particular, for harms. Our certainty in the evidence is very low for all outcomes. Overall survival was reported by eight studies (567 participants). Four studies reported survival rates at 12 months which ranged between 48% and 59%, and one study reported an overall survival rate of 50.5% at 24 months. The evidence is very uncertain about the effect of CAR T-cell therapy on overall survival. Two studies including 294 participants at baseline and 59 participants at the longest follow-up (12 months or 18 months) described improvements of quality of life measured with the EuroQol 5-Dimension 5-Level visual analogue scale (EQ-5D-5L VAS) or Function Assessment of Cancer Therapy-Lymphoma (FACT-Lym). The evidence is very uncertain about the effect of CAR T-cell therapy on quality of life. None of the studies reported treatment-related mortality. Five studies (550 participants) reported the occurrence of adverse events among participants, ranging between 99% and 100% for any grade adverse events and 68% to 98% for adverse events grade ≥ 3. In three studies (253 participants), 56% to 68% of participants experienced serious adverse events, while in one study (28 participants), no serious adverse events occurred. CAR T-cell therapy may increase the risk of adverse events and serious adverse events but the evidence is very uncertain about the exact risk. The occurrence of cytokine release syndrome (CRS) was reported in 11 studies (675 participants) under use of various grading criteria. Five studies reported between 42% and 100% of participants experiencing CRS according to criteria described in Lee 2014. CAR T-cell therapy may increase the risk of CRS but the evidence is very uncertain about the exact risk. Nine studies (575 participants) reported results on progression-free survival, disease-free survival or relapse-free survival. Twelve-month progression-free survival rates were reported by four studies and ranged between 44% and 75%. In one study, relapse-free survival remained at a rate of 64% at both 12 and 18 months. The evidence is very uncertain about the effect of CAR T-cell therapy on progression-free survival. Thirteen studies (620 participants) provided data on complete response rates. At six months, three studies reported complete response rates between 40% and 45%. The evidence is very uncertain about the effect of CAR T-cell therapy on complete response rates.

AUTHORS' CONCLUSIONS

The available evidence on the benefits and harms of CAR T-cell therapy for people with r/r DLBCL is limited, mainly because of the absence of comparative clinical trials. The results we present should be regarded in light of this limitation and conclusions should be drawn very carefully. Due to the uncertainty in the current evidence, a large number of ongoing investigations and a risk of substantial and potentially life-threatening complications requiring supplementary treatment, it is critical to continue evaluating the evidence on this new therapy.

Tissue sodium content in patients with systemic lupus erythematosus: association with disease activity and markers of inflammation

OBJECTIVES

Sodium (Na⁺) is stored in the skin and muscle and plays an important role in immune regulation. In animal models, increased tissue Na⁺ is associated with activation of the immune system, and high salt intake exacerbates autoimmune disease and worsens hypertension. However, there is no information about tissue Na⁺ and human autoimmune disease. We hypothesized that muscle and skin Na⁺ content is (a) higher in patients with systemic lupus erythematosus (SLE) than in control subjects, and (b) associated with blood pressure, disease activity, and inflammation markers (interleukin (IL)-6, IL-10 and IL-17 A) in SLE.

METHODS

Lower-leg skin and muscle Na⁺ content was measured in 23 patients with SLE and in 28 control subjects using ²³Na⁺ magnetic resonance imaging. Demographic and clinical information was collected from interviews and chart review, and blood pressure was measured. Disease activity was assessed using the SLE Disease Activity Index (SLEDAI). Plasma inflammation markers were measured by multiplex immunoassay.

RESULTS

Muscle Na⁺ content was higher in patients with SLE (18.8 (16.7-18.3) mmol/L) than in control subjects (15.8 (14.7-18.3) mmol/L; p < 0.001). Skin Na⁺ content was also higher in SLE patients than in controls, but this difference was not statistically significant. Among patients with SLE, muscle Na⁺ was associated with SLEDAI and higher concentrations of IL-10 after adjusting for age, race, and sex. Skin Na⁺ was significantly associated with systolic blood pressure, but this was attenuated after covariate adjustment.

CONCLUSION

Patients with SLE had higher muscle Na⁺ content than control subjects. In patients with SLE, higher muscle Na⁺ content was associated with higher disease activity and IL-10 concentrations.

Association of estimated sodium and potassium intake with blood pressure in patients with systemic lupus erythematosus

Sodium and potassium intake are modifiable determinants of hypertension in the general population but have not been studied in patients with systemic lupus erythematosus (SLE). We examined the relationship between urinary excretion of sodium and potassium, as an estimate of intake, and blood pressure in patients with SLE. We studied 178 SLE patients and 86 controls, matched for age, sex, and race. Urine sodium (Na⁺) and potassium (K⁺) were measured by flame photometry. Blood pressure was the average of two resting measurements. The associations between systolic (SBP) and diastolic blood pressures (DBP) and estimated 24-hour urinary Na⁺, K⁺, and Na⁺:K⁺ ratio were tested. The estimated mean 24-hour urinary K⁺ excretion was lower, and the Na⁺:K⁺ ratio was higher in patients with SLE than controls. There were no significant differences in the estimated 24-hour urinary Na⁺. In patients with SLE, a higher urinary Na⁺:K⁺ ratio was associated with higher SBP (β coefficient = 4.01, p = 0.023) and DBP (β coefficient = 4.41, p = 0.002) after adjusting for age, sex, and race. SLE patients had significantly lower estimated 24-hour urinary K⁺ and higher estimated 24-hour urinary Na⁺: K⁺ ratio than controls. The urinary Na⁺:K⁺ ratio was significantly associated with SBP and DBP.

GlycA, a novel marker of inflammation, is elevated in systemic lupus erythematosus

BACKGROUND

GlycA is a novel marker of systemic inflammation detected by nuclear magnetic resonance (NMR) spectroscopy. In the general population, GlycA is correlated with inflammatory markers such as C-reactive protein (CRP) and associated with coronary heart disease and diabetes. The utility of GlycA in patients with systemic lupus erythematosus (SLE) has not been defined. Therefore, we tested the hypothesis that GlycA concentrations are elevated in patients with SLE and associated with other markers of inflammation and coronary atherosclerosis.

METHODS

We compared concentrations of GlycA, detected by NMR, in 116 patients with SLE and 84 control subjects frequency-matched for age, sex, and race. SLE disease activity index (SLEDAI) and the SLE Collaborating Clinics damage index (SLICC) were calculated. Acute phase reactants, a panel of cytokines, and a lipid panel were measured. Electron beam computer tomography (EBCT) was used to quantify coronary artery calcification, a measure of coronary artery atherosclerosis.

RESULTS

Patients with SLE had higher concentrations of GlycA (398 (350-445)) than control subjects (339 (299-391)) µmol/L, p < 0.001. In patients with SLE, concentrations of GlycA were significantly associated with sedimentation rate (rho = 0.43), C-reactive protein (rho = 0.59), e-selectin (rho = 0.28), intracellular adhesion molecule-1 (rho = 0.30), triglycerides (rho = 0.45), all p < 0.0023 to account for multiple comparisons, but not with creatinine, SLEDAI, SLICC, or coronary calcium scores.

CONCLUSIONS

Concentrations of GlycA are higher in patients with SLE than control subjects and associated with markers of inflammation but not with SLE disease activity or chronicity scores or coronary artery calcification.

Genetic variation and coronary atherosclerosis in patients with systemic lupus erythematosus

Coronary artery disease is the major cause of mortality in patients with systemic lupus erythematosus (SLE). Increased cardiovascular risk in SLE is not explained by traditional risk factors. We examined the hypothesis that genetic variation contributes to the presence of coronary atherosclerosis in patients with SLE. The genotypes of single-nucleotide polymorphisms (SNP) in 152 candidate genes linked with autoimmune or cardiovascular risk were determined in 125 patients with SLE. Coronary artery calcium (CAC), a measure of coronary atherosclerosis, was detected in 32 patients (26%) by electron-beam computed tomography. Polymorphism in 20 of the candidate genes (ADAM33, ADIPOQ, CCL5, CCR7, CDKN2B, CSF1, IL4, IL12A, IL23R, INS, IRF5, MIF, MS4A1, PTGS1, PTPN22, RETN, SELE, TNFSF4, TNFRSF11B, and VCAM1) were nominally associated with the presence of CAC (p-values = 0.001-0.047 after adjustment for age, sex and race). Some of these are known susceptibility genes for SLE and others have been implicated in cardiovascular disease in other populations. No association withstood false discovery rate adjustment. Replication studies in additional cohorts of patients with SLE may be informative.

Free fatty acids are associated with metabolic syndrome and insulin resistance but not inflammation in systemic lupus erythematosus

Free fatty acids (FFAs) are implicated in the pathogenesis of insulin resistance and atherosclerosis. Inflammatory cytokines promote lipolysis and increase FFAs, a cause of endothelial dysfunction and increased atherosclerosis risk. We hypothesized that increased inflammation is associated with increased FFAs, resulting in insulin resistance and atherosclerosis in patients with systemic lupus erythematosus (SLE). We measured clinical variables, serum FFAs, homeostasis model assessment for insulin resistance (HOMA), inflammatory cytokines, markers of endothelial activation, cholesterol concentrations and coronary artery calcium in 156 patients with SLE and 90 controls. We compared FFAs in patients with SLE and controls using Wilcoxon rank sum tests and further tested for the independent association between FFAs and disease status with adjustment for age, race and sex using multivariable regression models. We assessed the relationship between FFAs and continuous variables of interest using Spearman correlation and multivariable regression analysis. Levels of FFAs were higher in patients with SLE than controls (0.55 mmol/l (0.37-0.71) vs 0.44 mmol/l (0.32-0.60), P = 0.02). Levels of FFAs remained significantly higher among patients with SLE after adjustment for age, race and sex (P = 0.03) but not after further adjustment for body mass index (P = 0.13). FFA levels did not differ according to the usage of current immunosuppressive medications in univariate and adjusted analysis (all P > 0.05). Among patients with SLE, concentrations of FFAs were higher among those with metabolic syndrome compared to those without (0.66 mmol/l (0.46-0.81) vs 0.52 mmol/l (0.35-0.66), P < 0.001). FFAs were positively correlated with insulin resistance (HOMA) (rho = 0.23, P = 0.004, P adjusted = 0.006) and triglyceride levels (rho = 0.22, P = 0.01, P adjusted = 0.004). FFAs were not associated with inflammatory cytokines (IL-6, TNF-α) (all P > 0.05) but were positively associated with levels of E-selectin (rho = 0.33, P = < 0.001, P adjusted = 0.001) and ICAM-1 (rho = 0.35, P < 0.001, P adjusted = 0.001). FFAs were correlated with coronary artery calcium score (rho = 0.20, P = 0.01) but this was attenuated after adjustment for age, race and sex (P = 0.33). From our study we concluded that FFAs are elevated in patients with SLE, particularly those with metabolic syndrome. FFAs in patients with SLE are not associated with markers of generalized inflammation but are associated with insulin resistance and markers of endothelial activation.

Cystatin C is associated with inflammation but not atherosclerosis in systemic lupus erythematosus

BACKGROUND

Even mild renal impairment is associated with increased atherosclerosis and cardiovascular mortality. Cystatin C, a novel measure of renal function, is more sensitive than conventional creatinine-based measures for the detection of subtle renal impairment. Increased cystatin concentrations are also associated with cardiovascular risk, independently of conventional measures of renal function. This study examined the hypothesis that cystatin C is elevated in systemic lupus erythematosus (SLE) and is associated with coronary atherosclerosis.

METHODS

Serum cystatin C, creatinine, tumor necrosis factor (TNF)-α, interleukin (IL)-6, coronary artery calcium score (CACS), Framingham risk score (FRS), Modified Diet in Renal Disease estimated glomerular filtration rate (MDRD-eGFR), and other clinical parameters were measured in 118 patients with SLE and 83 control subjects. The independent association between concentrations of cystatin C and SLE was evaluated using multivariable linear regression models, and the relationship between renal measures and coronary calcium was assessed with multivariable proportional odds logistic regression models.

RESULTS

Cystatin C, but not other measures of renal function, was significantly higher in patients with SLE than in controls (1.09 [interquartile range, IQR: 0.85-1.28] mg/l vs. 0.89 [IQR: 0.76-0.99] mg/l; p < 0.001 after adjustment for age, race, sex and MDRD-eGFR). Cystatin C was significantly associated with SLICC (p = 0.04), erythrocyte sedimentation rate (ESR) (p = 0.02), TNF-α (p = 0.008) and IL-6 (p = 0.01) after adjustment for age, race, and sex. Cystatin C was not significantly correlated with coronary calcium score in SLE (rho=0.096, p = 0.31) and the association remained non-significant after adjustment for age, race, sex, and Framingham risk score (p = 0.99).

CONCLUSIONS

Cystatin C was higher in patients with SLE than in control subjects even after adjustment for conventional measures of renal function. Cystatin C was significantly correlated with several markers of inflammation in SLE but was not associated with coronary atherosclerosis. Subtle renal dysfunction does not appear to be directly associated with accelerated atherosclerosis in SLE.

Novel cardiovascular risk prediction models in patients with systemic lupus erythematosus

Women with systemic lupus erythematosus (SLE) have increased risk for coronary heart disease (CHD) which is underestimated by the Framingham risk score (FRS). We hypothesized that new risk scores that include inflammation or vascular age in the risk calculation would better identify women with SLE at risk for CHD, particularly in those with subclinical coronary atherosclerosis. We calculated the FRS and Reynolds risk score (RRS) in 121 women with SLE and 65 age-matched female controls; coronary age-modified risk scores (camFRS, camRRS) were calculated using coronary age derived from the coronary artery calcium (CAC) score. Risk scores were compared in SLE and controls, and in SLE patients with and without CAC. Although CAC was present in 21 SLE patients (17%) and four controls (6%) (p = 0.033); the FRS, camFRS, RRS, and camRRS, did not differ significantly among SLE and controls (p > 0.05), but were all significantly higher in SLE patients with CAC compared with those without (p < 0.001 for all). The camFRS (8%, p = 0.016) but not camRRS (5%, p = 0.221) assigned significantly more SLE patients to a category of  ≥ 10% risk than conventional FRS (1%) and RRS (2%). The RRS was of limited use but coronary age may improve CHD risk prediction in SLE.

Adipocytokines in systemic lupus erythematosus: relationship to inflammation, insulin resistance and coronary atherosclerosis

We tested the hypothesis that concentrations of adipocytokines are altered in SLE and associated with coronary atherosclerosis, insulin resistance and inflammation. Concentrations of resistin, leptin, adiponectin and visfatin were measured in 109 patients with SLE and 78 control subjects. Coronary calcification was measured using electron beam-computed tomography, and insulin resistance was defined by the homeostasis model assessment index. Concentrations of adiponectin (28.7 +/- 17.9 vs 22.0 +/- 15.3 microg/mL, P = 0.003), leptin (41.1 +/- 49.9 vs 19.8 +/- 24.6 ng/mL, P < 0.001) and visfatin (7.5 +/- 10.5 vs 4.5 +/- 2.8 ng/mL, P < 0.001) were higher in patients with SLE than in controls. These differences remained significant after adjustment for age, race, sex and body mass index (BMI; all P values < 0.02). Concentrations of resistin (10.7 +/- 7.6 vs 9.1 +/- 5.1 ng/mL, P = 0.41) did not differ in patients and controls. In patients with SLE, leptin was positively associated with BMI (rho = 0.80, P < 0.001), insulin resistance (rho = 0.46, P < 0.001) and C-reactive protein (CRP) (rho = 0.30, P = 0.002), whereas adiponectin was negatively associated with the same factors (rho = -0.40, P < 0.001; rho = -0.38, P < 0.001; rho = -0.22, P = 0.02, respectively). None of the adipocytokines were associated with coronary atherosclerosis in SLE. In conclusion, patients with SLE have increased concentrations of adiponectin, leptin and visfatin. Lower concentrations of adiponectin and higher concentrations of leptin are associated with insulin resistance, BMI and CRP in patients with SLE.

Oxidative stress in systemic lupus erythematosus: relationship to disease activity and symptoms

Oxidative stress may play a role in the pathogenesis of systemic lupus erythematosus (SLE). We examined the hypothesis that oxidative stress was associated with indices of lupus disease activity and severity of symptoms. Urinary F2 isoprostane excretion, a validated marker of oxidative stress, was measured in 95 patients with SLE and 103 healthy controls. Outcome measures included SLEDAI and SLICC scores, the modified health assessment questionnaire, the fatigue severity scale (FSS), and visual analogue scales (VAS) for fatigue, pain and overall disease activity. F2 isoprostane excretion was compared in patients and controls, and its relationship with clinical variables in SLE examined. F2 isoprostane excretion did not differ significantly among patients with lupus (2.7 +/- 2.3 ng/mg Cr) and control subjects (2.2 +/- 1.4 ng/mg Cr) (P = 0.70). In patients with lupus, F2 isoprostane concentrations were independently associated with higher patient reported disease activity (VAS) (OR = 1.52, P = 0.01), fatigue (FSS, OR = 1.52, P = 0.03) and lower quality of life (OR = 0.73, P = 0.05), but not with objective markers or inflammation or disease activity. In conclusion, F2 isoprostane excretion is associated with patient-reported symptoms in SLE but not with measures of inflammation, SLEDAI or SLICC. Oxidative stress may contribute to debilitating symptoms such as fatigue in SLE.

Cardiovascular risk scores and the presence of subclinical coronary artery atherosclerosis in women with systemic lupus erythematosus

The Framingham risk score is widely used to identify patients at increased cardiovascular risk, and women with systemic lupus erythematosus (SLE) have a marked increased prevalence of cardiovascular events. Thus, we examined the hypothesis that cardiovascular risk scores would identify women with SLE who had asymptomatic coronary atherosclerosis. Ninety-three women with SLE and 65 control subjects were studied. The Framingham score and a score for younger populations developed from the Pathobiological Determinants of Atherosclerosis in Youth (PDAY) study were compared in both groups. Coronary atherosclerosis was ascertained by electron beam computed tomography. There were no significant differences in the median (interquartile range) Framingham [5 (2-10) compared to 7 (0-10), P = 0.88] and PDAY [15 (14-18) compared to 16 (13-18), P = 0.99] scores in patients with SLE and controls, respectively. Coronary atherosclerosis was associated with higher Framingham [12 (3-15) compared to 4 (1-8), P = 0.008] and PDAY [17 (15-19 compared to 15 (12-18), P = 0.03)] scores in patients with SLE; however, 99% of patients were classified as low-risk with a 10-year predicted risk of 1% (<1-3%). Our data indicate that cardiovascular risk scores are not adequate for risk stratification in women with SLE. Measurement of coronary calcification may add information to identify asymptomatic women with lupus who might benefit from aggressive preventive measures.

Plasma leptin concentrations and lipid profiles during nicotine abstinence

BACKGROUND

Weight gain is a frequent consequence of smoking cessation. Leptin, the protein product of the obese gene, seems to regulate appetite and body fat stores. The purpose of this study was to assess changes in circulating leptin levels and lipid metabolism during nicotine abstinence (NA) and their role in postcessation weight gain.

METHODS

Six sedentary, weight-stable, nonobese adult smokers were studied before and after 7 days of NA while following a weight-maintenance diet of standard composition. All subjects refrained from smoking overnight (as assessed by breath CO) and were instructed to chew nicotine polacrilex gum (4 mg) hourly from 7:00 AM to 8:00 PM [nicotine intake (NI) day]. Venous blood samples were collected at 7:00 AM (after an overnight fast) and 5:00 PM (pre-supper) on NI day and again after 7 days of NA.

RESULTS

Body weight did not change after 7 days of NA (72.0 +/- 2.8 versus 71.8 +/- 2.7 kg). Serum cotinine levels declined from 207 +/- 40 ng/mL during NI to undetectable levels during NA (P < 0.01). Fasting plasma leptin was similar during NI and NA (5.7 +/- 1.4 versus 6.4 +/- 1.9 ng/mL; P = NS). Moreover, plasma concentrations of glucose, insulin, and free fatty acids were unaffected by 7 days of NA. Although plasma triglycerides, total cholesterol, and low-density lipoprotein cholesterol were similar during NI and NA, high-density lipoprotein cholesterol increased by 15% after 7 days of NA (P < 0.05).

CONCLUSIONS

In this group of nonobese, adult smokers consuming an isocaloric diet, NA for 7 days did not affect body weight or circulating concentrations of leptin, glucose, insulin, or free fatty acids. In contrast, HDL cholesterol increased significantly after NA. These results indicate that under controlled dietary conditions, changes in leptin expression do not contribute to the weight gain that commonly accompanies smoking cessation.

Isolation of protein bodies on sucrose gradients

Storage protein bodies from sunflower cotyledons during early stages of seed germination were isolated on sucrose density gradients by isopycnic centrifugation. The density of this organelle on the gradients ranged between 1.26 and 1.36 g cm(-3). A proteinase with a pH optimum of 5.2 was associated with this organelle, and is probably responsible for degradation of storage protein. A NADH-dependent cytochrome-c reductase, a membrane marker enzyme with a pH optimum of 8.4, was also present in this organelle fraction.

Isolation of Plastids from Sunflower Cotyledons during Germination

Plastids from cotyledons of sunflower (Helianthus annus L.) seedlings, germinated in the dark or in the light, were isolated by isopycnic sucrose density gradient centrifugation. At all stages of development the whole plastids contained triose phosphate isomerase, NADPH-glyoxylate reductase, and l-dihydroxyphenylalanine oxidase, which were used as marker enzymes. At the beginning of germination the isopycnic density of whole plastids (proplastids) was about 1.22 g cm(-3). During development of proplastids into etioplasts in the dark, their isopycnic density increased to 1.26 g cm(-3). During exposure of germinating seedlings to white light for 2 days, the isopycnic density of whole plastids decreased from 1.26 to 1.22 g cm(-3). These changes in isopycnic density of plastids on sucrose density gradients are consistent with changes in the plastid ultrastructure caused by the protein-rich prolamellar body or by the lipid-rich thylakoids. Broken plastids (thylakoids), determined by the main peak of chlorophyll, increased in isopycnic density from less than 1.14 to about 1.17 g cm(-3) during illumination. During germination no major changes occurred in the isopycnic density of mitochondria. Microbodies had an isopycnic density of 1.24 g cm(-3) in very early stages of germination, and their density increased to 1.265 g cm(-3), when glyoxysomal enzymes reached maximum development.

Development of Microbodies in Sunflower Cotyledons and Castor Bean Endosperm during Germination

In cotyledons of sunflower seedlings glyoxysomal and peroxisomal enzymes exhibit different rates of development during germination. The total activity of isocitrate lyase, a glyoxysomal marker enzyme, rapidly increased during the first 3 days, and then decreased 89% by day 9. Exposure to light accelerated this decrease only slightly. The specific activity of glyoxysomal enzymes (malate synthetase, isocitrate lyase, citrate synthetase, and aconitase) in the microbody fraction from sucrose density gradients increased between days 2 and 4 about 2- to 3-fold, and thereafter it remained about constant in light or darkness.Total activity of the peroxisomal enzymes increased slowly in the dark during the first 4 days of germination and thereafter remained at a constant level of activity in the dark or increased 2-fold in 24 hours of light. The specific activties of glycolate oxidase, hydroxypyruvate reductase, and serine-glyoxylate aminotransferase in the isolated microbody fraction increased about 10-fold between days 2 and 4 in the dark and then remained constant or increased again 10-fold after an additional 48 hours in the light.The total activity of the common microbody marker, catalase, developed similarly to isocitrate lyase, but decreased only 72% by day 9. The specific activities of enzymes (catalase, malate dehydrogenase, and aspartate aminotransferase) common to both microbody systems were 10- to 1000-fold greater than those of other enzymes. It is proposed that malate and aspartate may be involved in hydrogen transport between microbodies and other cellular sites.Glutamate-glyoxylate aminotransferase was very active in microbodies from castor bean endosperm and sunflower cotyledons. The specific activity of this aminotransferase developed similarly to glyoxysomal enzymes in the dark but further increased in the light, as did peroxisomal enzymes.The microbody fraction of castor bean endosperm germinated in the dark for 5 days contained both glyoxysomal and peroxisomal enzymes of similar specific activity.Adjacent to the microbody fraction on sucrose gradients from sunflower cotyledons were etioplasts at slightly lower densities and protein bodies at similar and higher densities. Their presence in the microbody fractions resulted in artificially low specific activities.

A survey of plants for leaf peroxisomes

Leaves of 10 plant species, 7 with photorespiration (spinach, sunflower, tobacco, pea, wheat, bean, and Swiss chard) and 3 without photorespiration (corn, sugarcane, and pigweed), were surveyed for peroxisomes. The distribution pattern for glycolate oxidase, glyoxylate reductase, catalase, and part of the malate dehydrogenase indicated that these enzymes exist together in this organelle. The peroxisomes were isolated at the interface between layers of 1.8 to 2.3 m sucrose by isopycnic nonlinear sucrose density gradient centrifugation or in 1.95 m sucrose on a linear gradient. Chloroplasts, located by chlorophyll, and mitochondria by cytochrome c oxidase, were in 1.3 to 1.8 m sucrose. In leaf homogenates from the first 7 species with photorespiration, glycolate oxidase activity ranged from 0.5 to 1.5 mumoles x min(-1) x g(-1) wet weight or a specific activity of 0.02 to 0.05 mumole x min(-1) x mg(-1) protein. Glyoxylate reductase activity was comparable with glycolate oxidase. Catalase activity in the homogenates ranged from 4000 to 12,000 mumoles x min(-1) x g(-1) wet weight or 90 to 300 mumoles x min(-1) x mg(-1) protein. Specific activities of malate dehydrogenase and cytochrome oxidase are also reported. In contrast, homogenates of corn and sugarcane leaves, without photorespiration, had 2 to 5% as much glycolate oxidase, glyoxylate reductase, and catalase activity. These amounts of activity, though lower than in plants with photorespiration, are, nevertheless, substantial. Peroxisomes were detected in leaf homogenates of all plants tested; however, significant yields were obtained only from the first 5 species mentioned above. From spinach and sunflower leaves, a maximum of about 50% of the marker enzyme activities was found to be in these microbodies after homogenization. The specific activity for peroxisomal glycolate oxidase and glyoxylate reductase was about 1 mumole x min(-1) x mg(-1) protein; for catalase. 8000 mumoles x min(-1) x mg(-1) protein, and for malate dehydrogenase, 40 mumoles x min(-1) x mg(-1) protein. Only small to trace amounts of marker enzymes for leaf peroxisomes were recovered on the sucrose gradients from the last 5 species of plants. Bean leaves, with photorespiration, had large amounts of these enzymes (0.57 mumole of glycolate oxidase x min(-1) x g(-1) tissue) in the soluble fraction, but only traces of activity in the peroxisomal fraction. Low peroxisome recovery from certain plants was attributed to particle fragility or loss of protein as well as to small numbers of particles in such plants as corn and sugarcane. Homogenates of pigweed leaves (no photorespiration) contained from one-third to one-half the activity of the glycolate pathway enzymes as found in comparable preparations from spinach leaves which exhibit photorespiration. However, only traces of peroxisomal enzymes were separated by sucrose gradient centrifugation of particles from pigweed. Data from pigweed on the absence of photorespiration yet abundance of enzymes associated with glycolate metabolism is inconsistent with current hypotheses about the mechanism of photorespiration. Most of the catalase and part of the malate dehydrogenase activity was located in the peroxisomes. Contrary to previous reports, the chloroplast fractions from plants with photo-respiration did not contain a concentration of these 2 enzymes, after removal of peroxisomes by isopycnic sucrose gradient centrifugation.