Dyskalemia in people at increased risk for heart failure: findings from the heart 'OMics' in AGEing (HOMAGE) trial

AIMS

In people at risk of heart failure (HF) enrolled in the Heart 'OMics' in AGEing (HOMAGE) trial, spironolactone reduced circulating markers of collagen synthesis, natriuretic peptides, and blood pressure and improved cardiac structure and function. In the present report, we explored factors associated with dyskalaemia.

METHODS AND RESULTS

The HOMAGE trial was an open-label study comparing spironolactone (up to 50 mg/day) versus standard care in people at risk for HF. After randomization, serum potassium was assessed at 1 and 9 months and was defined as low when ≤3.5 mmol/L (hypokalaemia) and high when ≥5.5 mmol/L (hyperkalaemia). Multivariable logistic regression models were constructed to identify clinical predictors of dyskalaemia. A total of 513 participants (median age 74 years, 75% men, median estimated glomerular filtration rate 71 mL/min/1.73 m² ) had serum potassium available and were included in this analysis. At randomization, 88 had potassium < 4.0 mmol/L, 367 had potassium 4.0-5.0 mmol/L, and 58 had potassium > 5.0 mmol/L. During follow-up, on at least one occasion, a serum potassium < 3.5 mmol/L was observed in 6 (1.2%) and <4.0 mmol/L in 46 (9%) participants, while a potassium > 5.0 mmol/L was observed in 38 (8%) and >5.5 mmol/L in 5 (1.0%) participants. The median (percentile_25-75 ) increase in serum potassium with spironolactone during the study was 0.23 (0.16; 0.29) mmol/L. Because of the low incidence of dyskalaemia, for regression analysis, hypokalaemia and hyperkalaemia thresholds were set at <4.0 and >5.0 mmol/L, respectively. The occurrence of a serum potassium > 5.0 mmol/L during follow-up was positively associated with the presence of diabetes mellitus {odds ratio [OR]: 1.21 [95% confidence interval (CI) 2.14; 3.79]} and randomization to spironolactone (OR: 2.83 [95% CI 1.49; 5.37]). Conversely, the occurrence of a potassium concentration < 4.0 mmol/L was positively associated with the use of thiazides (OR: 2.39 [95% CI 1.32; 4.34]), blood urea concentration (OR: 2.15 [95% CI 1.34; 3.39] per 10 mg/dL), and history of hypertension (OR: 2.32 [95% CI 1.02; 5.29]) and negatively associated with randomization to spironolactone (OR: 0.30 [95% CI 0.18; 0.52]).

CONCLUSIONS

In people at risk for developing HF and with relatively normal renal function, spironolactone reduced the risk of hypokalaemia and, at the doses used, was not associated with the occurrence of clinically meaningful hyperkalaemia.

Primary and Secondary Outcome Reporting in Randomized Trials: JACC State-of-the-Art Review

Consensus as to best practices for the selection, reporting, and interpretation of primary and secondary outcomes of randomized controlled trials is lacking. We reviewed the strategies adopted in publications of randomized controlled trials (RCTs) for the analysis, presentation, and interpretation of efficacy outcomes from a survey of all cardiovascular RCTs published in the New England Journal of Medicine, Lancet, and the Journal of the American Medical Association during 2019. We focus on the choice of primary outcomes, the variety of approaches to selecting secondary outcomes, the options sometimes used to control type I error, and the common practice to not correct for multiple testing in reporting secondary outcomes. We comment on current practice across journals in the reporting of P values and also how conclusions in trial reports frequently adhere to an undue reliance on P < 0.05 as a basis for positive claims of treatment efficacy. We conclude with recommendations for how future RCT reports could best select, report, and interpret their findings on primary and secondary outcomes.

The effect of spironolactone on cardiovascular function and markers of fibrosis in people at increased risk of developing heart failure: the heart 'OMics' in AGEing (HOMAGE) randomized clinical trial

Aims 

To investigate the effects of spironolactone on fibrosis and cardiac function in people at increased risk of developing heart failure.

Methods and results 

Randomized, open-label, blinded-endpoint trial comparing spironolactone (50 mg/day) or control for up to 9 months in people with, or at high risk of, coronary disease and raised plasma B-type natriuretic peptides. The primary endpoint was the interaction between baseline serum galectin-3 and changes in serum procollagen type-III N-terminal pro-peptide (PIIINP) in participants assigned to spironolactone or control. Procollagen type-I C-terminal pro-peptide (PICP) and collagen type-1 C-terminal telopeptide (CITP), reflecting synthesis and degradation of type-I collagen, were also measured. In 527 participants (median age 73 years, 26% women), changes in PIIINP were similar for spironolactone and control [mean difference (mdiff): −0.15; 95% confidence interval (CI) −0.44 to 0.15 μg/L; P = 0.32] but those receiving spironolactone had greater reductions in PICP (mdiff: −8.1; 95% CI −11.9 to −4.3 μg/L; P < 0.0001) and PICP/CITP ratio (mdiff: −2.9; 95% CI −4.3 to −1.5; <0.0001). No interactions with serum galectin were observed. Systolic blood pressure (mdiff: −10; 95% CI −13 to −7 mmHg; P < 0.0001), left atrial volume (mdiff: −1; 95% CI −2 to 0 mL/m²; P = 0.010), and NT-proBNP (mdiff: −57; 95% CI −81 to −33 ng/L; P < 0.0001) were reduced in those assigned spironolactone.

Conclusions 

Galectin-3 did not identify greater reductions in serum concentrations of collagen biomarkers in response to spironolactone. However, spironolactone may influence type-I collagen metabolism. Whether spironolactone can delay or prevent progression to symptomatic heart failure should be investigated.

BDNF in the Aged Brain: Translational Implications for Parkinson's Disease

Brain Derived Neurotrophic Factor (BDNF) is a member of the neurotrophin family of secreted growth factors. BDNF signaling is known to exert both chronic, pro-survival effects related to gene expression and protein synthesis ("canonical signaling"), and acute effects as a modulator of neurotransmission ("non-canonical signaling"). BDNF has received a great deal of attention for its role in neurodegenerative diseases including Huntington's Disease (HD), Alzheimer's Disease (AD), and Parkinson's Disease (PD) and has been extensively reviewed elsewhere in this regard (e.g., [1-6]). However aging-related changes in BDNF function and expression have been studied only rarely, with the majority of studies characterizing changes in structures such as the hippocampus and neocortex. In this review, we attempt to briefly summarize the extent of the existing literature on age-related BDNF changes, and discuss the relevance of these changes as a factor potentially impacting therapeutics in aged parkinsonian subjects.

Metabolic Energy Capacity of Dopaminergic Grafts and the Implanted Striatum in Parkinsonian Nonhuman Primates as Visualized with Cytochrome Oxidase Histochemistry

Histochemistry for visualization of the mitochondrial enzyme cytochrome oxidase has been used to detect cellular and regional differences in brain energy metabolism. We have examined the pattern of cytochrome oxidase (CO) staining in grafts of embryonic ventral mesencephalic tissue, and in the implanted striatum, of MPTP-treated monkeys as one index of the functional activity of grafted tissue and its influence on the host brain. Four monkeys were selected for study based on interesting variations in dopamine (DA) neuron content of their bilateral grafts as demonstrated with tyrosine-hydroxylase (TH) immunocytochemistry. The results suggest that grafts rich in DA neurons increase the metabolic activity of the implanted striatum of DA-depleted monkeys, and that this improvement of local energy metabolism is greater in the vicinity of grafts containing greater numbers of DA neurons. In addition, the pattern of CO staining within tissue transplants indicates that DA neurons exhibit the highest rate of metabolic activity among all cell types contained in the ventral mesencephalic grafts, and that the transplants receive metabolically active innervation from outside or within the grafted tissue.

Intrastriatal Grafts from Multiple Donors do not Result in a Proportional Increase in Survival of Dopamine Neurons in Nonhuman Primates

We examined the potential for “double grafts,” i.e., grafts from two donors in each recipient, to enhance the total number of ventral mesencephalic dopamine neurons that survive grafting in adult African green monkeys. Because dopamine cell survival in grafts represents a small percentage of the total number of neurons grafted, several human clinical trials recently have employed grafts of tissue from multiple donors (e.g., from two to eight embryos per host recipient) in attempts to increase the total number of dopamine neurons that survive in grafts. Presumably, this is intended to elevate dopamine levels by providing more dopamine neurons to the damaged brain to alleviate the symptoms of parkinsonism. While well-developed grafts with several thousand dopamine neurons were found in most recipient animals, we observed a reduced total number of tyrosine hydroxylase positive neurons in the grafts in spite of the presence of some double grafts that were larger than normal. The overall growth of the grafts was impressive; some grafts were so large that they spanned the full dorsoventral extent of the caudate nucleus, probably reflecting the fact that twice as much tissue was implanted in each drop site in comparison to our standard protocol. However, some animals revealed atypical patterns of neurite outgrowth that appeared limited to the grafted tissue, and at least one monkey revealed “amorphous” grafts generally lacking in cellular structure, which suggests a possible rejection phenomenon. These findings raise questions about the use of multiple donors and suggest that the likelihood of rejection and/or cell death may be enhanced, which is of potential importance in the design of grafting strategies for clinical applications.

Acute kidney injury in stable COPD and at exacerbation

BACKGROUND

While acute kidney injury (AKI) alone is associated with increased mortality, the incidence of hospital admission with AKI among stable and exacerbating COPD patients and the effect of concurrent AKI at COPD exacerbation on mortality is not known.

METHODS

A total of 189,561 individuals with COPD were identified from the Clinical Practice Research Datalink. Using Poisson and logistic regressions, we explored which factors predicted admission for AKI (identified in Hospital Episode Statistics) in this COPD cohort and concomitant AKI at a hospitalization for COPD exacerbation. Using survival analysis, we investigated the effect of concurrent AKI at exacerbation on mortality (n=36,107) and identified confounding factors.

RESULTS

The incidence of AKI in the total COPD cohort was 128/100,000 person-years. The prevalence of concomitant AKI at exacerbation was 1.9%, and the mortality rate in patients with AKI at exacerbation was 521/1,000 person-years. Male sex, older age, and lower glomerular filtration rate predicted higher risk of AKI or death. There was a 1.80 fold (95% confidence interval: 1.61, 2.03) increase in adjusted mortality within the first 6 months post COPD exacerbation in patients suffering from AKI and COPD exacerbation compared to those who were AKI free.

CONCLUSION

In comparison to previous studies on general populations and hospitalizations, the incidence and prevalence of AKI is relatively high in COPD patients. Coexisting AKI at exacerbation is prognostic of poor outcome.

Neuroprotective potential of pleiotrophin overexpression in the striatonigral pathway compared with overexpression in both the striatonigral and nigrostriatal pathways

Intrastriatal injection of recombinant adeno-associated viral vector serotype 2/1 (rAAV2/1) to overexpress the neurotrophic factor pleiotrophin (PTN) provides neuroprotection for tyrosine hydroxylase immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc), increases THir neurite density in the striatum (ST) and reverses functional deficits in forepaw use following 6-hydroxydopamine (6-OHDA) toxic insult. Glial cell line-derived neurotrophic factor (GDNF) gene transfer studies suggest that optimal neuroprotection is dependent on the site of nigrostriatal overexpression. The present study was conducted to determine whether enhanced neuroprotection could be accomplished via simultaneous rAAV2/1 PTN injections into the ST and SN compared with ST injections alone. Rats were unilaterally injected in the ST alone or injected in both the ST and SN with rAAV2/1 expressing either PTN or control vector. Four weeks later, all rats received intrastriatal injections of 6-OHDA. Rats were euthanized 6 or 16 weeks relative to 6-OHDA injection. A novel selective total enumeration method to estimate nigral THir neuron survival was validated to maintain the accuracy of stereological assessment. Long-term nigrostriatal neuroprotection and functional benefits were only observed in rats in which rAAV2/1 PTN was injected into the ST alone. Results suggest that superior preservation of the nigrostriatal system is provided by PTN overexpression delivered to the ST and restricted to the ST and SN pars reticulata and is not improved with overexpression of PTN within SNpc neurons.

Stimulation of the rat subthalamic nucleus is neuroprotective following significant nigral dopamine neuron loss

Deep brain stimulation of the subthalamic nucleus (STN-DBS) is efficacious in treating the motor symptoms of Parkinson's disease (PD). However, the impact of STN-DBS on the progression of PD is unknown. Previous preclinical studies have demonstrated that STN-DBS can attenuate the degeneration of a relatively intact nigrostriatal system from dopamine (DA)-depleting neurotoxins. The present study examined whether STN-DBS can provide neuroprotection in the face of prior significant nigral DA neuron loss similar to PD patients at the time of diagnosis. STN-DBS between 2 and 4 weeks after intrastriatal 6-hydroxydopamine (6-OHDA) provided significant sparing of DA neurons in the SN of rats. This effect was not due to inadvertent lesioning of the STN and was dependent upon proper electrode placement. Since STN-DBS appears to have significant neuroprotective properties, initiation of STN-DBS earlier in the course of PD may provide added neuroprotective benefits in addition to its ability to provide symptomatic relief.

Embryonic substantia nigra grafts in the mesencephalon send neurites to the host striatum in non-human primate after overexpression of GDNF

In spite of partial success in treating Parkinson's disease by using ectopically placed grafts of dopamine-producing cells, restoration of the original neuroanatomical circuits, if possible, might work better. Previous evidence of normal anatomic projections from ventral mesencephalic (VM) grafts placed in the substantia nigra (SN) has been limited to neonatal rodents and double grafting or bridging procedures. This study attempted to determine whether injection of a potent growth-promoting factor, glial cell line-derived neurotrophic factor (GDNF), into the target regions or placement of fetal striatal co-grafts in the nigrostriatal pathway might elicit neuritic outgrowth to the caudate nucleus. Four adult St. Kitts green monkeys received embryonic VM grafts into the rostral mesencephalon near the host SN, and injections of adeno-associated virus 2 (AAV2)/GDNF or equine infectious anemia virus (EIAV)/GDNF into the caudate. Three adult monkeys were co-grafted with fetal VM tissue near the SN and fetal striatal grafts (STR) 2.5 mm rostral in the nigrostriatal pathway. Before sacrifice, the striatal target regions were injected with the retrograde tracer Fluoro-Gold (FG). FG label was found in tyrosine hydroxylase-labeled neurons in VM grafts in the SN of only those monkeys that received AAV2/GDNF vector injections into the ipsilateral striatum. All monkeys showed FG labeling in the host SN when FG labeling was injected on the same side. These data show that grafted dopaminergic neurons can extend neurites to a distant target releasing an elevated concentration of GDNF, and suggest that grafted neurons can be placed into appropriate loci for potential tract reconstruction.

The synaptic impact of the host immune response in a parkinsonian allograft rat model: Influence on graft-derived aberrant behaviors

Graft-induced dyskinesias (GIDs), side-effects found in clinical grafting trials for Parkinson's disease (PD), may be associated with the withdrawal of immunosuppression. The goal of this study was to determine the role of the immune response in GIDs. We examined levodopa-induced dyskinesias (LIDs), GID-like behaviors, and synaptic ultrastructure in levodopa-treated, grafted, parkinsonian rats with mild (sham), moderate (allografts) or high (allografts plus peripheral spleen cell injections) immune activation. Grafts attenuated amphetamine-induced rotations and LIDs, but two abnormal motor syndromes (tapping stereotypy, litter retrieval/chewing) emerged and increased with escalating immune activation. Immunohistochemical analyses confirmed immune activation and graft survival. Ultrastructural analyses showed increases in tyrosine hydroxylase-positive (TH+) axo-dendritic synapses, TH+ asymmetric specializations, and non-TH+ perforated synapses in grafted, compared to intact, striata. These features were exacerbated in rats with the highest immune activation and correlated statistically with GID-like behaviors, suggesting that immune-mediated aberrant synaptology may contribute to graft-induced aberrant behaviors.

Embryonic substantia nigra grafts show directional outgrowth to cografted striatal grafts and potential for pathway reconstruction in nonhuman primate

Transplantation of embryonic dopamine (DA) neurons has been tested as a therapy for Parkinson's disease. Most studies placed DA neurons into the striatum instead of the substantia nigra (SN). Reconstruction of this DA pathway could serve to establish a more favorable environment for control of DA release by grafted neurons. To test this we used cografts of striatum to stimulate growth of DA axons from embryonic SN that was implanted adjacent to the host SN in African green monkeys. Embryonic striatum was implanted at one of three progressive distances rostral to the SN. Immunohistochemical analysis revealed DA neuron survival and neuritic outgrowth from the SN grafts at 12-36 weeks after grafting. Each animal showed survival of substantial numbers of DA neurons. Most fibers that exited SN grafts coursed rostrally. Striatal grafts showed evidence of target-directed outgrowth and contained dense patterns of DA axons that could be traced from their origin in the SN grafts. A polarity existed for DA neurites that exited the grafts; that is, those seen caudal to the grafts did not appear to be organized into a directional outflow while those on the rostral side were arranged in linear profiles coursing toward the striatal grafts. Some TH fibers that reached the striatal grafts appeared to arise from the residual DA neurons of the SN. These findings suggest that grafted DA neurons can extend neurites toward a desired target over several millimeters through the brain stem and caudal diencephalon of the monkey brain, which favors the prospect of circuit reconstruction from grafted neurons placed into appropriate locations in their neural circuitry. Further study will assess the degree to which this approach can be used to restore motor balance in the nonhuman primate following neural transplantation.

A rapid access cardiology service for chest pain, heart failure and arrhythmias accurately diagnoses cardiac disease and identifies patients at high risk: a prospective cohort study

OBJECTIVE

To conduct a one year follow up study of patients seen in a combined rapid access chest pain, arrhythmia and heart failure clinic.

METHODS

Local general practitioners, accident and emergency department clinicians and other hospital clinicians were invited to refer patients with a new presentation of chest pain, palpitations and suspected cardiac-induced breathlessness to the rapid access cardiology clinics at Charing Cross Hospital, London, on a one-stop, no appointment basis. Consent to be followed up by a postal questionnaire one year later was sought from all patients attending between 1 November 2002 and 31 October 2003.

RESULTS

1223 patients were seen in the 12 month study period. 940 (77%) consented to one year follow up. 216 (23%) patients had a diagnosis of definite cardiac, 621 (66%) of not cardiac and 103 of possible cardiac disease (11%). 98% of patients diagnosed "not cardiac" did not receive a diagnosis of cardiac disease over the following 12 months. Of patients with diagnosed definite cardiac disease, one year cardiac mortality was 7 of 216 (3%), compared with an age- and sex-matched expected cardiac mortality of 0.9% (standardised mortality ratio 3.5, 95% confidence interval (CI) 1.4 to 7.2). For patients with an initial diagnosis of possible or not cardiac disease, cardiac mortality at one year was 0.3% compared with an expected cardiac mortality of 0.4% (standardised mortality ratio 0.8, 95% CI 0.1 to 2.8).

CONCLUSIONS

A rapid access cardiology clinic accurately diagnoses and risk stratifies patients into those with cardiac disease at high risk of cardiac death and those without significant cardiac disease.

Rapid access arrhythmia clinic for the diagnosis and management of new arrhythmias presenting in the community: a prospective, descriptive study

OBJECTIVE

To investigate whether a rapid access approach is useful for the evaluation of patients with symptoms suggestive of a new cardiac arrhythmia.

DESIGN

Prospective, descriptive study.

SETTING

Secondary care based rapid access arrhythmia clinic in West London, UK.

PARTICIPANTS

Patients referred by their general practitioner or the emergency department with symptoms suggestive of a new cardiac arrhythmia.

MAIN OUTCOME MEASURES

Number of patients with a newly diagnosed significant arrhythmia. Number of patients with diagnosed atrial fibrillation. Number of eligible, moderate, and high risk patients treated with warfarin.

RESULTS

Over a 25 month period 984 referrals were assessed. The mean age was 55 years (range 20-90 years) and 56% were women. The median time from referral to assessment was one day. A significant cardiac arrhythmia was newly diagnosed in 40% of patients referred to the RAAC. The most common arrhythmia was atrial fibrillation, with 203 new cases (21%). Of these, 74% of eligible patients over 65 were treated with warfarin. Other arrhythmias diagnosed were supraventricular tachycardias (127 (13%)), conduction disorders (43 (4%)), and non-sustained ventricular tachycardia (21 (2%)). Vasovagal syncope was diagnosed for 53 patients (5%). The most frequent diagnosis was symptomatic ventricular and supraventricular extrasystoles (355 (36%)).

CONCLUSION

A rapid access arrhythmia clinic is an innovative approach to the diagnosis and management of new cardiac arrhythmias in the community. It provides a rapid diagnosis, stratifies risk, and leads to prompt initiation of effective treatment for this population.

A clonal line of mesencephalic progenitor cells converted to dopamine neurons by hematopoietic cytokines: a source of cells for transplantation in Parkinson's disease

Neural progenitor cells potentially provide a limitless, on-demand source of cells for grafting into patients with Parkinson's disease (PD) if the signals needed to control their conversion into dopamine (DA) neurons could be identified. We have recently shown that cytokines which instruct cell division and differentiation within the hematopoeitic system may provide similar functions in the central nervous system. We have shown that mitotic progenitor cells can be isolated from embryonic rat mesencephalon and that these cells respond to a combination of interleukin-1, interleukin-11, leukemia inhibitory factor, and glial cell line-derived neurotrophic factor yielding a tyrosine hydroxylase-immunoreactive (THir) phenotype in 20-25% of total cells. In the present study, 24 clonal cell lines derived from single cells of mesencephalic proliferation spheres were examined for their response to the cytokine mixture. The clone yielding the highest percentage of THir neurons (98%) was selected for further study. This clone expressed several phenotypic characteristics of DA neurons and expression of Nurr1. The response to cytokines was stable for several passages and after cryopreservation for several months. When grafted into the striatum of DA-depleted rats, these cells attenuated rotational asymmetry to the same extent as freshly harvested embryonic DA neurons. These data demonstrate that mesencephalic progenitor cells can be clonally expanded in culture and differentiated in the presence of hematopoietic cytokines to yield enriched populations of DA neurons. When transplanted, these cells provide significant functional benefit in the rat model of PD.

Tumor necrosis factor alpha is toxic to embryonic mesencephalic dopamine neurons

Levels of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) are increased in postmortem brain and cerebral spinal fluid from patients with Parkinson's disease (PD). This observation provides a basis for associating TNFalpha with neurodegeneration, but a specific toxicity in dopamine (DA) neurons has not been firmly established. Therefore, we investigated TNFalpha-induced toxicity in DA neurons by utilizing primary cultures of embryonic rat mesencephalon. Exposure to TNFalpha resulted in a dose-dependent decrease in DA neurons as evidenced by decreased numbers of tyrosine hydroxylase-immunoreactive (THir) cells. TNFalpha toxicity was selective for DA neurons in that neither glial cell counts nor the total number of neurons was decreased and no general cytotoxicity was evidenced by lactate dehydrogenase assay. Many of the cells which remained immunoreactive for TH had shrunken and rounded cell bodies with broken, blunted, or absent processes. However, TNFalpha-treated cultures also contained some THir cells which appeared to be undamaged and possibly resistant to TNFalpha-induced toxicity. Additionally, immunocytochemistry revealed basal expression of TNFalpha receptor 1 (p55, R1) and TNFalpha receptor 2 (p75, R2) on all cells within the mesencephalic cultures to some degree, even though only DA neurons were affected by TNFalpha treatment. These data strongly suggest that TNFalpha mediates cell death in a sensitive population of DA neurons and support the potential involvement of proinflammatory cytokines in the degeneration of DA neurons in PD.

Diminished survival of mesencephalic dopamine neurons grafted into aged hosts occurs during the immediate postgrafting interval

The survival rate of dopamine (DA) neurons in mesencephalic grafts to young adult rats is poor, estimated at 5-20%, and even poorer in grafts to the aged striatum. Grafted cells die in young adult rats during the first 4 days after implantation. The present study was undertaken to determine whether the decreased survival of DA neurons in grafts to aged rats is (1) due to additional cell death during the immediate postgrafting interval or (2) due to protracted cell loss during longer postgrafting intervals. We compared survival rates of tyrosine hydroxylase-immunoreactive (THir) neurons in cell suspension grafts to young adult (3 months) and aged (24 months) male Fischer 344 rats at 4 days and 2 weeks after transplantation. At 4 days after grafting, mesencephalic grafts within the aged rat striatum contain approximately 25% of the number of THir neurons in the same mesencephalic cell suspension grafted to young adult rats. This corroborates the decreased survival of grafted DA neurons we have demonstrated previously at 10 weeks postgrafting. THir neurons in grafts to the intact striatum possessed a significantly shorter "long axis" than their counterparts on the lesioned side. No significant differences in the number of apoptotic nuclear profiles or total alkaline phosphatase staining between mesencephalic grafts to young and aged rats were detectable at 4 days postgrafting. In summary, the present study indicates that the exaggerated cell death of grafted DA neurons that occurs following implantation to the aged striatum occurs during the immediate postgrafting interval, timing identical to that documented for young adult hosts.

Oligodendrocyte-type 2 astrocyte-derived trophic factors increase survival of developing dopamine neurons through the inhibition of apoptotic cell death

Survival of embryonic dopamine (DA) neurons is extremely low (5-20%) following transplantation. Strategies to increase this survival are critical to the future of transplantation for Parkinson's disease. We demonstrate here that a factor(s) released from striatal oligodendrocyte-type 2 astrocytes (SO2A) greatly improves the survival and phenotype expression of mesencephalic DA neurons in culture while simultaneously decreasing the presence of apoptotic nuclear profiles, as detected by the TUNEL method and bisbenzamide/tyrosine hydroxylase double labeling. This SO2A-derived trophic factor(s) has minimal effects on glia and no effect on nondopaminergic mesencephalic neurons. The developmental period during which this SO2A trophic effect occurs (E14-18) coincides with the period when mesencephalic grafts are undergoing the highest rates of apoptosis, i.e., immediately following implantation. Therefore, SO2A-derived trophic factor(s) offers great potential for the augmentation of grafted DA neuron survival.

Cyclosporin A protects striatal neurons in vitro and in vivo from 3-nitropropionic acid toxicity

The neuroprotective properties of cyclosporin A (CsA) are mediated by its ability to prevent mitochondrial permeability transition during exposure to high levels of calcium or oxidative stress. By using the mitochondrial toxin 3-nitropropionic acid (3NP), the present study assessed whether CsA could protect striatal neurons in vitro and in vivo. In vitro, 3NP produced a 20-30% reduction of striatal glutamic acid decarboxylase-immunoreactive (GAD-ir) neurons. A single treatment with CsA protected GAD-ir neurons from 3NP toxicity at lower (0.2 or 1.0 microM), but not at higher (5.0 microM) doses. Similar findings were seen when the cultures were treated twice with cyclosporin. In vivo experiments used the Lewis rat model of Huntington's disease (HD) in which a low 3NP dose was delivered subcutaneously through an osmotic minipump. Rats received unilateral or bilateral intrastriatal saline injections to disrupt the blood-brain barrier (BBB) and facilitate CsA reaching vulnerable neurons. In the first experiment, CsA treated 3NP-lesioned rats displayed significantly more dopamine-and adenosine-3;, 5;-monophosphate-regulated phosphoprotein (DARPP32-ir) neurons ipsilateral to BBB disruption compared to the contralateral intact striatum, indicating that disruption of the BBB maybe necessary for CsA's neuroprotective effects. In the second experiment, stereological counts of DARPP32-ir neurons revealed that CsA protected striatal neurons in a dose-dependent manner following bilateral disruption of the striatal BBB. Rats treated with the higher (15 or 20 mg/kg) but not lower (5 mg/kg) doses of CsA displayed greater numbers of DARRP32-ir striatal neurons relative to vehicle-treated 3NP-lesioned rats. Thus, under conditions in which CsA can gain access to striatal neurons, significant protection from 3NP toxicity is observed. Therefore, CsA or more lipophilic analogues of this compound, may be of potential therapeutic benefit by protecting vulnerable neurons from the primary pathological event observed in HD.

Time course of apoptotic cell death within mesencephalic cell suspension grafts: implications for improving grafted dopamine neuron survival

The vast majority ( congruent with 90%) of embryonic mesencephalic dopamine (DA) neurons die following transplantation to the striatum. Recent reports indicate that at least a subpopulation of grafted cells undergo apoptotic cell death at early times following implantation. This study examines the temporal pattern and magnitude of apoptotic cell death following the implantation of mesencephalic cell suspension grafts. Two techniques, a modified terminal deoxynucleotide-mediated nucleotide end labeling (TUNEL) technique and cresyl violet staining, are used to assess apoptotic cell death by detection of its biochemical and morphological identifiers, respectively. Male, Fischer 344 rats were examined at 1, 4, 7, and 28 days following implantation of embryonic day 14 (E14) ventral mesencephalic cells to the DA-denervated striatum. Results indicate that the overwhelming majority of apoptotic cell death occurs within the first 7 days after transplantation. However, the impact of the apoptosis that occurs over the first week following grafting only appears to limit grafted tyrosine hydroxylase-immunoreactive (THir) neuron survival during the first 4 days. No significant differences between the survival rates of THir neurons at 4 days after grafting and at 28 days after grafting were found. Therefore, it appears that the critical interval during which an estimated 90% of grafted DA neurons die is during the first 4 days postimplantation and that a major contributor to this cell death is apoptosis.

Striatal dopaminergic correlates of stable parkinsonism and degree of recovery in old-world primates one year after MPTP treatment

Despite widespread use of the primate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease, there is a paucity of data concerning the relationship between striatal dopaminergic function and behavior over time. This study examines the relationship between markers of dopamine neuron integrity and dopaminergic metabolic activity in striatal subregions with the degree of parkinsonian disability in 32 monkeys treated with MPTP one year earlier. Based on the parkinsonian summary score during the month following MPTP treatment, each monkey was assigned to one of four severity categories. We called these categories "Severe", "Moderate", "Mild" and "Asymptomatic". Monkeys in the Severe category were behaviorally stable, and loss of dopamine concentration was greater than 98% in all subregions of striatum one year after MPTP treatment. This value was not significantly different from the level of depletion, reported previously, at one to two months after MPTP in Severe monkeys, and apparently this loss of striatal dopamine is beyond the level from which effective compensations can occur. The parkinsonian disabilities in monkeys of other severity groups (Moderate, Mild, Asymptomatic) improved significantly over the year, despite having mean dopamine depletion of 75-99% in different subregions of striatum at one to two months after MPTP treatment. At one year after MPTP treatment, the mean dopamine depletions in different subregions of caudate nucleus and putamen had diminished in Asymptomatics (21-81%), Milds (35-96%), and Moderates (86-97%). Dopamine loss in nucleus accumbens was relatively spared compared with most striatal subregions, yet in Severe monkeys the decrease in this region reached 96%. In addition, at one year after MPTP treatment, there was a significant linear relationship between parkinsonian behavioral severity category and dopamine concentration, and homovanillic acid concentration and homovanillic acid/dopamine ratio in the striatum. The re-establishment of dopamine levels and homovanillic acid/dopamine ratios was most pronounced in putamen, ventromedial caudate nucleus and nucleus accumbens. Thus the small difference in striatal dopamine loss that distinguishes monkeys with widely different behavior at one to two months after MPTP increases over time. We suggest that the milder the initial loss, the greater capacity there is for regeneration or sprouting of dopamine terminals, which is reflected in marked increases in dopamine levels and modest elevations of metabolic activity (homovanillic acid/dopamine ratio). With greater initial losses, there is less capacity to increase terminal density, which is reflected later by smaller increases in striatal dopamine levels and more marked increases in metabolic activity. It appears that 5-10% of normal striatal dopamine levels is sufficient for overtly normal motor performance in non-human primates.

Striatal trophic activity is reduced in the aged rat brain

Our previous studies demonstrated that the survival of a mesencephalic graft was reduced in aged animals suggesting an age-related decline in target-derived neurotrophic activity. We tested this hypothesis by examining dopamine (DA) and trophic activities from the striatum of intact or unilateral 6-hydroxydopamine (6-OHDA) lesioned rats of increasing age. Fisher 344 rats were 4, 12, 18, and 23 months old (m.o.) at sacrifice. Half the animals had received unilateral 6-OHDA lesions of the mesostriatal DA pathway 8 weeks earlier. Striatal tissue punches were analyzed for DA, homovanillic acid (HVA), and DA activity (HVA/DA) using HPLC. The remainder of the striatal tissue was homogenized to generate tissue extracts which were added to E14.5 ventral mesencephalic cultures to test trophic activity. In the non-lesioned animals, striatal DA was reduced and striatal DA activity was increased in the 18 and 23 m.o. animals relative to the 4 and 12 m.o. animals. Striatal trophic activity was inversely related to age. In the lesioned animals, striatal DA ipsilateral to 6-OHDA infusion was below detection limits while the contralateral striatum exhibited age-related changes in DA similar to those seen in the non-lesioned animals. In 4 m.o. lesioned rats, striatal trophic activity ipsilateral to 6-OHDA infusion was elevated by 26% relative to the contralateral side. The ipsi/contra-lateral differences in striatal trophic activity were reduced in 12 m.o. animals and absent in the 18 and 23 m.o. groups. These data suggest that advancing age is associated with a reduction in striatal DA as well as trophic activity. Moreover, the aged striatum loses its ability to biochemically and trophically compensate for DA reduction and therefore may represent a more challenging environment for the survival, growth, and function of a fetal graft.

Diminished viability, growth, and behavioral efficacy of fetal dopamine neuron grafts in aging rats with long-term dopamine depletion: an argument for neurotrophic supplementation

We examined the behavioral and morphological correlates of the response to a single intrastriatal dispersed cell graft of fetal rat ventral mesencephalic tissue in male Fischer-344 rats of varying age (4, 17, and 24-26 months old) and history of mesostriatal dopamine (DA) depletion (1 or 14 months). Our goal was to determine the impact of advancing age and duration of DA depletion in the host on DA graft viability and function. The findings can be summarized as follows. (1) Fetal DA neuron grafts that were effective in completely ameliorating amphetamine-induced rotational behavior in young rats with short-term lesions were virtually without effect in aged rats with long-term lesions. Middle-aged rats with long-term lesions responded to these grafts with partial behavioral recovery. (2) Age of the host at the time of transplantation, and not duration of DA depletion, was the primary determinant of response to DA grafts. (3) Diminished efficacy of grafts in lesioned aging rats was related to decreased survival and neurite extension of transplanted DA neurons. (4) Co-grafts of DA neurons with Schwann cells as a source of neurotrophic support improved the behavioral outcome of grafts in aged lesioned rats. These findings support the view that the DA-depleted striatum of aged rats is an impoverished environment for survival, growth, and function of DA grafts. Consistent with this view, local supplementation of the neurotrophic environment of grafted DA neurons with products of co-grafted Schwann cells, a demonstrated source of neurotrophic activity for embryonic DA neurons, improved graft outcome.

Therapeutic potential of nerve growth factors in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative syndrome which primarily affects dopamine-producing neurons of the substantia nigra, resulting in poverty and slowness of movement, instability of gait and posture, and tremor at rest in individuals with the disease. While symptoms of the disease can be effectively managed for several years with available drugs, the syndrome is progressive and the efficacy of standard drugs wanes with time. One experimental approach to therapy is to use natural and synthetic molecules which promote survival and growth of dopaminergic neurons, so-called 'neurotrophic factors', to stabilise the diminishing population of dopaminergic neurons and stimulate compensation and growth in these cells. In this review, we examine the available evidence on 29 molecules with neurotrophic properties for dopaminergic neurons. The properties of these molecules provide ample reasons for optimism that a neurotrophic strategy can be developed that would provide a significant treatment option for patients with PD. While the search continues for even more specific, potent and long lasting agents, the single greatest challenge is the development of techniques for targeted delivery of these molecules.

Co-grafted embryonic striatum increases the survival of grafted embryonic dopamine neurons

To enhance the current therapeutic benefit of dopamine (DA) neuron grafts in Parkinson's disease, strategies must be developed that increase both DA neuron survival and fiber outgrowth into the denervated striatum. Previous work in our laboratory has demonstrated that dopaminergic neurons grow to greater size when co-grafted with striatal cell suspensions and display extensive tyrosine hydroxylase-positive (TH+) projections, but no conclusion could be reached concerning enhancement of survival of grafted DA neurons. The aim of the present study was to characterize further the potential trophic effects of striatal co-grafts on grafted mesencephalic DA neuron survival. Unilaterally lesioned male Fischer 344 rats were grafted with either a suspension of mesencephalic cells or with both mesencephalic and striatal cell suspensions. Co-grafts were either mixed together or placed separately into the striatum. Lesioned rats receiving no graft served as controls. Rotational behavior was assessed following amphetamine challenge at 2 weeks prior to grafting and at 4 and 8 weeks following grafting. Only rats receiving co-grafts of nigral and striatal suspensions separated by a distance of 1 mm showed significant behavioral recovery from baseline rotational asymmetry. Both mixed and separate striatal co-grafts were associated with a doubling of DA neuron survival compared with solo mesencephalic grafts. In the mixed co-graft experiment, DA neurite branching appeared enhanced and TH-rich patches were observed, whereas with co-grafts that were separated, TH+ innervation of the intervening host striatum was increased significantly. These results provide the first evidence suggesting that nigral-striatal co-grafts, particularly those placed separately and in proximity to each other, increase both DA neuron survival and neurite extension from the mesencephalic component of the grafts.

Pattern of synaptophysin immunoreactivity within mesencephalic grafts following transplantation in a parkinsonian primate model

The majority of investigations into the degree of restoration of neural circuitry following transplantation of the embryonic ventral mesencephalon to the striatum have focused upon the particular neurochemical subtypes of the fibers exchanged between graft and host. Visualization of neurites of specific neurotransmitter type while informative regarding the specificity of graft-host interactions, vastly underrepresents overall synaptogenesis as it may occur in the grafting situation. The present approach of using a molecular marker characteristic of all normal, functional synapses provides broader information about the synaptic remodeling that occurs after tissue grafting. Synaptophysin (SY), an integral membrane protein of the synaptic vesicle, is a reliable marker of nerve terminal differentiation. Immunohistochemical staining with antibodies directed against SY and the dopamine synthetic enzyme tyrosine hydroxylase (TH) was used to assess overall synaptic differentiation as well as the relationship between SY immunoreactivity and the distribution of grafted dopamine (DA) neurons and processes in mesencephalic grafts and mesencephalic-striatal co-grafts implanted in the striatum of MPTP-treated African green monkeys. Grafted embryonic cerebellar tissue was used as a comparison graft type that does not normally exchange prominent direct projections with striatum. Dense pericellular arrays of SY-positive terminals were associated with TH-positive neurons in mesencephalic grafts. In mixed mesencephalic-striatal co-grafts, TH-positive fiber patches within the striatal portion of the graft demonstrated a high degree of correspondence with SY immunoreactivity. In contrast, grafts of cerebellar tissue did not display the same pattern of prominent pericellular arrays of SY staining. These observations suggest that functional synapses are abundantly present within grafted mesencephalon, and that these contacts are enriched in areas of the graft occupied by DA neurons. Implantation of an inappropriate striatal target, the cerebellum, results in visibly diminished innervation. The pattern of SY labeling observed suggests that tissue grafts are extensively innervated, probably both from extrinsic and intrinsic sources, and that the pattern and density of this innervation corresponds to the appropriateness of the graft-host interaction.

Intrastriatal grafts from multiple donors do not result in a proportional increase in survival of dopamine neurons in nonhuman primates

We examined the potential for "double grafts," i.e., grafts from two donors in each recipient, to enhance the total number of ventral mesencephalic dopamine neurons that survive grafting in adult African green monkeys. Because dopamine cell survival in grafts represents a small percentage of the total number of neurons grafted, several human clinical trials recently have employed grafts of tissue from multiple donors (e.g., from two to eight embryos per host recipient) in attempts to increase the total number of dopamine neurons that survive in grafts. Presumably, this is intended to elevate dopamine levels by providing more dopamine neurons to the damaged brain to alleviate the symptoms of parkinsonism. While well-developed grafts with several thousand dopamine neurons were found in most recipient animals, we observed a reduced total number of tyrosine hydroxylase positive neurons in the grafts in spite of the presence of some double grafts that were larger than normal. The overall growth of the grafts was impressive; some grafts were so large that they spanned the full dorsoventral extent of the caudate nucleus, probably reflecting the fact that twice as much tissue was implanted in each drop site in comparison to our standard protocol. However, some animals revealed atypical patterns of neurite outgrowth that appeared limited to the grafted tissue, and at least one monkey revealed "amorphous" grafts generally lacking in cellular structure, which suggests a possible rejection phenomenon. These findings raise questions about the use of multiple donors and suggest that the likelihood of rejection and/or cell death may be enhanced, which is of potential importance in the design of grafting strategies for clinical applications.

Differential regulation of astrocytic mRNAs in the rat striatum after lesions of the cortex or substantia nigra

This study evaluates the time course of expression of three astrocytic mRNAs, glial fibrillary acidic protein (GFAP), apolipoprotein E (ApoE), and clusterin, in the rat striatum (ST) following a unilateral lesion of either the cortex (CX) or the substantia nigra (SN), using Northern blot and in situ hybridization analyses. We found that while there was a time-dependent increase in astrocytic GFAP mRNA in the deafferented ST following both the CX and the SN lesions, the time course of the response was different between the two lesion paradigms. Specifically, the increase in GFAP mRNA in striatal astrocytes after the SN lesion was rapid and transient returning to control levels by 10 days postlesion, while the response was long lasting and remained increased until at least 27 days after the CX lesion. In addition, the mRNA response for both ApoE and clusterin was differentially regulated in response to the two lesions. Specifically, both clusterin and ApoE mRNAs were rapidly increased in the ST following the CX lesion while both mRNAs remained unchanged following the SN lesion. Data from this study extend information derived from previous investigations on the multifunctional role of astrocytes in the response to brain injury. Specifically, our data support the notion that while the time course of the GFAP response in striatal astrocytes may vary between lesion paradigms, the upregulation of GFAP is part of a generalized response of reactive astrocytes to diverse brain injuries. By comparison, upregulation of the mRNAs for the lipoproteins clusterin and ApoE are lesion specific and may play a role in the transport of recycled myelin lipids from dying axons to actively growing axons and dendrites in reactive synaptogenesis.

Metabolic energy capacity of dopaminergic grafts and the implanted striatum in parkinsonian nonhuman primates as visualized with cytochrome oxidase histochemistry

Histochemistry for visualization of the mitochondrial enzyme cytochrome oxidase has been detect cellular and regional differences in brain metabolism. We have examined the pattern of cytochrome oxidase (CO) staining in grafts of embryonic ventral mesencephalic tissue, and in the implanted striatum, of MPTP-treated monkeys as one index of the functional activity of grafted tissue and its influence on the host brain. Four monkeys were selected for study based on interesting variations in dopamine (DA) neuron content of their bilateral grafts as demonstrated with tyrosine-hydroxylase (TH) immunocytochemistry. The results suggest that grafts rich in DA neurons increase the metabolic activity of the implanted striatum of DA-depleted monkeys, and that this improvement of local energy metabolism is greater in the vicinity of grafts containing greater numbers of DA neurons. In addition, the pattern of CO staining within tissue transplants indicates that DA neurons exhibit the highest rate of metabolic activity among all cell types contained in the ventral mesencephalic grafts, and that the transplants receive metabolically active innervation from outside or within the grafted tissue.

Functional fetal nigral grafts in a patient with Parkinson's disease: chemoanatomic, ultrastructural, and metabolic studies

A patient with Parkinson's disease received bilateral fetal human nigral implants from six donors aged 6.5 to 9 weeks post-conception. Eighteen months following a post-operative clinical course characterized by marked improvement in clinical function, this patient died from events unrelated to the grafting procedure. Post-mortem histological analyses revealed the presence of viable grafts in all 12 implant sites, each containing a heterogeneous population of neurons and glia. Approximately 210,146 implanted tyrosine hydroxylase-immunoreactive (TH-ir) neurons were found. A greater number of TH-ir grafted neurons were observed in the right (128,162) than the left (81,905) putamen. Grafted TH-ir neurons were organized in an organotypic fashion. These cells provided extensive TH-ir and dopamine transporter-ir innervation to the host striatum which occurred in a patch-matrix fashion. Quantitative evaluations revealed that fetal nigral grafts reinnervated 53% and 28% of the post-commissural putamen on the right and left side, respectively. Grafts on the left side innervated a lesser area of the striatum, but optical density measurements were similar on both sides. There was no evidence that the implants induced sprouting of host TH-ir systems. Electron microscopic analyses revealed axo-dendritic and occasional axo-axonic synapses between graft and host. In contrast, axo-somatic synapses were not observed. In situ hybridization for TH mRNA revealed intensely hybridized grafted neurons which far exceeded TH mRNA expression within residual host nigral cells. In addition, gamma-amino butyric acid (GABA)-ergic neurons were observed within the graft that formed a dense local neuropil which was confined to the implant site. Serotonergic neurons were not observed within the graft. Cytochrome oxidase activity was increased bilaterally within the grafted post-commissural putamen, suggesting increased metabolic activity. In this regard, a doubling of cytochrome oxidase activity was observed within the grafted post-commissural putamen bilaterally relative to the non-grafted anterior putamen. The grafts were hypovascular relative to the surrounding striatum and host substantia nigra. Blood vessels within the graft stained intensely for GLUT-1, suggesting that this marker of blood--brain barrier function is present within human nigral allografts. Taken together, these data indicate that fetal nigral neurons can survive transplantation, functionally reinnervate the host putamen, establish synaptic contacts with host neurons, and sustain many of the morphological and functional characteristics of normal nigral neurons following grafting into a patient with PD.

Functional fetal nigral grafts in a patient with Parkinson's disease: chemoanatomic, ultrastructural, and metabolic studies

A patient with Parkinson's disease received bilateral fetal human nigral implants from six donors aged 6.5 to 9 weeks post-conception. Eighteen months following a post-operative clinical course characterized by marked improvement in clinical function, this patient died from events unrelated to the grafting procedure. Post-mortem histological analyses revealed the presence of viable grafts in all 12 implant sites, each containing a heterogeneous population of neurons and glia. Approximately 210,146 implanted tyrosine hydroxylase-immunoreactive (TH-ir) neurons were found. A greater number of TH-ir grafted neurons were observed in the right (128,162) than the left (81,905) putamen. Grafted TH-ir neurons were organized in an organotypic fashion. These cells provided extensive TH-ir and dopamine transporter-ir innervation to the host striatum which occurred in a patch-matrix fashion. Quantitative evaluations revealed that fetal nigral grafts reinnervated 53% and 28% of the post-commissural putamen on the right and left side, respectively. Grafts on the left side innervated a lesser area of the striatum, but optical density measurements were similar on both sides. There was no evidence that the implants induced sprouting of host TH-ir systems. Electron microscopic analyses revealed axo-dendritic and occasional axo-axonic synapses between graft and host. In contrast, axo-somatic synapses were not observed. In situ hybridization for TH mRNA revealed intensely hybridized grafted neurons which far exceeded TH mRNA expression within residual host nigral cells. In addition, gamma-amino butyric acid (GABA)-ergic neurons were observed within the graft that formed a dense local neuropil which was confined to the implant site. Serotonergic neurons were not observed within the graft. Cytochrome oxidase activity was increased bilaterally within the grafted post-commissural putamen, suggesting increased metabolic activity. In this regard, a doubling of cytochrome oxidase activity was observed within the grafted post-commissural putamen bilaterally relative to the non-grafted anterior putamen. The grafts were hypovascular relative to the surrounding striatum and host substantia nigra. Blood vessels within the graft stained intensely for GLUT-1, suggesting that this marker of blood--brain barrier function is present within human nigral allografts. Taken together, these data indicate that fetal nigral neurons can survive transplantation, functionally reinnervate the host putamen, establish synaptic contacts with host neurons, and sustain many of the morphological and functional characteristics of normal nigral neurons following grafting into a patient with PD.

Early gestational mesencephalon grafts, but not later gestational mesencephalon, cerebellum or sham grafts, increase dopamine in caudate nucleus of MPTP-treated monkeys

The mechanism of the behavioral improvement observed in parkinsonian primates that receive intrastriatal transplants of fetal dopamine neurons has not been firmly established. Dopamine production by grafted neurons may be the basis of the behavioral recovery. Alternatively, stimulation of the host dopamine system by the transplant procedure itself may be central to the outcome. The present study examined whether dopamine concentration was raised in the caudate nucleus of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated primate following grafting, and if so, whether the elevation was dependent on either (i) the introduction of the implantation cannula (sham), (ii) the brain region that was grafted, or (iii) the gestational age of fetal tissue that was grafted. Transplantation of early gestational age fetal ventral mesencephalon (embryonic days 40-50) was associated with significant elevation of caudate nucleus dopamine concentration to a mean of approximately 20% of control values in the vicinity (within 2 mm) of the graft, compared with more distant sites in the caudate nucleus. With early gestational age fetal ventral mesencephalon, the ratio of homovanillic acid/dopamine concentration near the graft site was normalized compared to the elevated value found in the caudate nucleus distant from the graft site. Grafts of later stage fetal ventral mesencephalon, or fetal cerebellum, or sham implantation did not increase dopamine concentration or lower homovanillic acid/dopamine ratio near the graft site. Biochemical and histochemical evidence suggests that host dopamine neurons terminating in the nucleus accumbens are not the source of the changes. Numerous tyrosine hydroxylase-positive neurons at the graft site were only observed in the MPTP-treated monkeys that received grafts of early gestational age fetal ventral mesencephalon. These data lend strong support to the hypothesis that dopamine derived from grafted dopamine neurons is the major basis for behavioral recovery observed following intrastriatal transplantation in our MPTP-treated monkeys.

Astrocytes retrovirally transduced with BDNF elicit behavioral improvement in a rat model of Parkinson's disease

Neurotrophic factors that improve the survival of specific neuronal types during development and after exposure to various neuronal insults hold potential for treatment of neurodegenerative diseases. In particular, brain-derived neurotrophic factor (BDNF) has been shown to exert trophic and protective effects on dopaminergic neurons, the cell type known to degenerate in Parkinson's disease. To determine whether increased levels of biologically produced BDNF affect the function or regeneration of damaged dopaminergic neurons, the effects of grafting astrocytes transduced with the human BDNF gene into the striatum of the partially lesioned hemiparkinsonian rat were examined. Replication deficient retroviruses carrying either human prepro-BDNF or human alkaline phosphatase (AP) cDNA were used to transduce primary type 1 astrocytes purified from neonatal rat cortex. In vitro, BDNF mRNA was expressed by BDNF transduced astrocytes (BDNF astrocytes), but not control AP transduced astrocytes (AP astrocytes), as determined by reverse transcription polymerase chain reaction (RT-PCR). The modified astrocytes were injected into the right striatum 15 days after partial lesioning of the right substantia nigra with 6-hydroxydopamine. Transplantation of BDNF astrocytes, but not AP astrocytes, significantly attenuated amphetamine-induced rotation by 45% 32 days after grafting. Apomorphine-induced rotation increased over time in both groups, but was not significantly different in the BDNF-treated group. The modified BDNF astrocytes survived well with non-invasive growth in the brain for up to 42 days. Although BDNF mRNA positive cells were not detected within the graft site using in situ hybridization, alkaline phosphatase immunoreactive (IR) cells were present in control graft sites suggesting that the retroviral construct continued to be expressed at 42 days. Analysis of the density of tyrosine hydroxylase (TH)-IR fibers showed no effect of BDNF on TH-IR fiber density in the striatum on the lesioned side. These findings suggest that ex vivo gene therapy with BDNF ameliorates parkinsonian symptoms through a mechanism(s) other than one involving an effect of BDNF on regeneration or sprouting from dopaminergic neurons.

The detrimental effect of levodopa on behavioral efficacy of fetal dopamine neuron grafts in rats is reversible following prolonged withdrawal of chronic dosing

In previous studies, we observed that chronic levodopa treatment resulted in impaired morphology and function of grafted dopamine neurons in rats. To begin to better understand how levodopa treatment might influence dopamine neurons, we examined whether subsequent discontinuation of chronic levodopa treatment might allow for recovery of graft efficacy. Function of embryonic mesencephalic tissue grafts was assessed by monitoring rotational behavior elicited by amphetamine in lesioned, grafted rats initially treated for 6 weeks with levodopa followed by a 6 week drug-free period. As observed previously, control grafted animals, but not levodopa treated animals, showed behavioral improvement. However, following a 6 week withdrawal period, the levodopa animals demonstrated a significant reduction in amphetamine rotations which was reminiscent of control animals. This suggests that grafted neurons can recover functionally after levodopa treatment is withdrawn, which may be of significance in clinical transplantation trials.

Sham surgery does not ameliorate MPTP-induced behavioral deficits in monkeys

Parkinsonism has been reported to improve following transplantation of fetal mesencephalic tissue into the striatum of MPTP-exposed monkeys and humans and in patients with idiopathic Parkinson's disease. While there is good evidence for the survival of grafted tyrosine hydroxylase (TH)-positive cells in animal studies, it is not known whether they produce neuronal effects that account for behavioral improvement after transplantation or whether spontaneous or graft-induced changes in the host striatum are at least partly responsible. Are neuronal synaptic connections and dopamine release necessary, or would "toenails and talcum powder" do the job equally well? We have addressed these questions by studying several types of implantation surgeries, including sham surgery, the implantation of cerebellar tissue, and the implantation of mesencephalic TH-positive fetal tissue of various gestational ages into the striatum. Adult male African green monkeys received systemic MPTP administration (cumulative doses of 2.0-2.5 mg/kg) prior to these stereotaxic surgical manipulations. Subjects were matched for quantitative behavioral deficits prior to surgery. Subjects were examined and assessments made by "blinded" observers who scored individual spontaneous and elicited behaviors. Observers were trained and tested repeatedly for inter-rater reliability. A "parkinsonian summary score" derived and determined using a principal component factor analysis of a large sample of data from MPTP-treated and normal monkeys of the same species was used to assess behavior. Postmortem brain tissue was prepared for biochemical analysis of dopamine concentrations and TH immunohistochemical studies. The most dramatic improvement was seen in monkeys with "early" (< 4 cm fetal crown rump length) surviving substantia nigra grafts in the caudate nucleus. Some behavioral improvements were seen in MPTP-treated sham-operated monkeys, cerebellar-grafted monkeys, and "later" (> 14 cm fetal crown rump length) substantia nigra-grafted monkeys. These changes in monkeys which did not have surviving dopamine-producing grafts probably represent the recovery capacity of MPTP-treated host brain during this time interval since un-operated subjects showed similar changes. More variable effects were seen with substantia nigra grafts in the putamen. The most consistent correlate of behavioral improvement in all experimental groups was elevation in dopamine concentrations near the grafts compared with a distant striatal location which is believed to represent the depletion without the effects of the grafts. While these data do not establish the precise mechanism of action, they point to a hierarchy of factors which provide increasingly larger restorative effects, including sprouting of host neurons and increased dopamine production by grafted fetal dopamine neurons. Sham surgery appears to be significantly less effective than early fetal mesencephalic tissue which survives and releases dopamine.

Sham Surgery does not Ameliorate MPTP-Induced Behavioral Deficits in Monkeys

Parkinsonism has been reported to improve following transplantation of fetal mesencephalic tissue into the striatum of MPTP-exposed monkeys and humans and in patients with idiopathic Parkinson's disease. While there is good evidence for the survival of grafted tyrosine hydroxylase (TH)-positive cells in animal studies, it is not known whether they produce neuronal effects that account for behavioral improvement after transplantation or whether spontaneous or graft-induced changes in the host striatum are at least partly responsible. Are neuronal synaptic connections and dopamine release necessary, or would “toenails and talcum powder” do the job equally well? We have addressed these questions by studying several types of implantation surgeries, including sham surgery, the implantation of cerebellar tissue, and the implantation of mesencephalic TH-positive fetal tissue of various gestational ages into the striatum. Adult male African green monkeys received systemic MPTP administration (cumulative doses of 2.0-2.5 mg/kg) prior to these stereotaxic surgical manipulations. Subjects were matched for quantitative behavioral deficits prior to surgery. Subjects were examined and assessments made by “blinded” observers who scored individual spontaneous and elicited behaviors. Observers were trained and tested repeatedly for inter-rater reliability. A “parkinsonian summary score” derived and determined using a principal component factor analysis of a large sample of data from MPTP-treated and normal monkeys of the same species was used to assess behavior. Postmortem brain tissue was prepared for biochemical analysis of dopamine concentrations and TH immunohistochemical studies. The most dramatic improvement was seen in monkeys with “early” (<4 cm fetal crown rump length) surviving substantia nigra grafts in the caudate nucleus. Some behavioral improvements were seen in MPTP-treated sham-operated monkeys, cerebellar-grafted monkeys, and “later” (>14 cm fetal crown rump length) substantia nigra-grafted monkeys. These changes in monkeys which did not have surviving dopamine-producing grafts probably represent the recovery capacity of MPTP-treated host brain during this time interval since un-operated subjects showed similar changes. More variable effects were seen with substantia nigra grafts in the putamen. The most consistent correlate of behavioral improvement in all experimental groups was elevation in dopamine concentrations near the grafts compared with a distant striatal location which is believed to represent the depletion without the effects of the grafts. While these data do not establish the precise mechanism of action, they point to a hierarchy of factors which provide increasingly larger restorative effects, including sprouting of host neurons and increased dopamine production by grafted fetal dopamine neurons. Sham surgery appears to be significantly less effective than early fetal mesencephalic tissue which survives and releases dopamine.

Peripheral nerve-dopamine neuron co-grafts in MPTP-treated monkeys: augmentation of tyrosine hydroxylase-positive fiber staining and dopamine content in host systems

Previous studies of rats in our laboratory indicate that a molecule or molecules released by Schwann cells exert survival and growth-promoting effects on mesencephalic dopamine neurons. In the present study, we have begun to investigate the potential for Schwann cell augmentation of host dopamine fiber systems and embryonic dopamine neuron grafts in non-human primates. Ten adult male St Kitts African Green monkeys treated with the dopaminergic neurotoxin 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine one year previously, but behaviorally asymptomatic, served as hosts for implant studies. A segment of young adult monkey saphenous nerve was collected to serve as an implanted tissue source of Schwann cell-derived growth factors. Nerve was enclosed in a hollow semi-permeable polymer fiber for implantation into the lateral ventricle, with embryonic ventral mesencephalic tissue co-grafts containing developing dopamine neurons aimed at nearby locations in the caudate nucleus. Control implants consisted of an empty polymer fiber co-grafted with embryonic ventral mesencephalon. Our morphological observations indicate that while no clear augmentation of the morphology of grafted dopamine neurons attributable to co-grafted nerve was observed, this lack of influence may be related to the spatial separation of the co-grafted tissues. In contrast, some monkeys with nerve segments in the lateral ventricle exhibited increased tyrosine hydroxylase-positive fiber staining in the immediately adjacent lateral septal area and the ventricular wall of the caudate nucleus. This enhancement was not associated with empty polymer implants. Levels of dopamine and its metabolite homovanillic acid derived from tissue punches in the caudate nucleus and septal area support the view that monkeys exhibiting morphological enhancement of host dopamine systems also show biochemical increases in dopamine levels and changes in the direction of normalization of the homovanillic acid/dopamine ratio. Biochemical values from a single septal area tissue punch in one animal were an exception to this rule. This study suggests that while the utility of peripheral nerve as a source of dopamine graft augmentation in non-human primates remains to be demonstrated, grafted nerve has a stimulatory effect on host brain dopamine systems in adult, dopamine-depleted monkeys, and that this morphological effect can be dissociated from previously hypothesized injury-induced regeneration.

Cryopreservation and storage of embryonic rat mesencephalic dopamine neurons for one year: comparison to fresh tissue in culture and neural grafts

Blocks of embryonic rat ventral mesencephalic tissue containing the developing A8-A10 dopamine (DA) cell groups were cryopreserved and stored for approximately 1 year, at which time this tissue was thawed, dissociated into a cell suspension, and compared to a similar preparation of fresh mesencephalic tissue for viability in tissue culture and neural grafts. Estimates of total cell number immediately prior to plating in culture indicated that cryopreserved tissue yields fewer cells, but when this reduced cell number is compensated for, and equal numbers of cells were plated in culture, approximately equal total numbers of neurons, as well as tyrosine hydroxylase (TH)-positive neurons, were present in cultures from cryopreserved and fresh tissue. Grafting of equal numbers of fresh and cryopreserved mesencephalic cells into the striatum of adult rats with large unilateral lesions of the nigrostriatal DA pathway tended to yield smaller grafts with fewer surviving TH-positive cells with less extensive neuronal processes when tissue was previously cryopreserved. However, grafts derived from freeze-stored tissue provided a similar time-course and extent of behavioral recovery in amphetamine-induced rotational tests to that provided by fresh tissue grafts. Taken together, our findings indicate that while cryopreservation of mesencephalic tissue has its costs--reduced cell yield in cultures and grafts, and compromised morphology in grafts--sufficient numbers of cryopreserved neurons survive the grafting procedure to ameliorate behavioral signs of DA depletion in the lesioned rat model.

Fetal dopamine cell survival after transplantation is dramatically improved at a critical donor gestational age in nonhuman primates

Mesencephalic tissue containing newly generated dopamine neurons was collected from brains of embryonic African green monkeys at 44 and 49 days of gestation and stereotaxically implanted into multiple sites in the caudate nucleus of adult monkeys previously treated with the dopamine protoxin, 1-methyl-4-phenyl-1,2,3,6-tetrathydropyridine. Ultrasonography was utilized to assess the developmental stage prior to hysterotomy. Brains were removed for combined histochemical and biochemical analyses at 3 1/2 months after grafting to determine the extent of graft survival and growth. The dopamine content of the target nucleus was assessed from microdissected "punches" placed in proximity to grafts identified in unfixed brain slices prior to fixation. Tissue dopamine levels adjacent to the grafts were elevated markedly, reaching 25-50% of control levels at some sites in the caudate nucleus. Morphometric analysis of graft size and dopamine cell numbers was performed with computer-enhanced, video-based imaging. Exceptionally large grafts that far exceeded their initial size at the time of implantation were seen at each placement site. The dopamine cell count was as high as 3500 in a single graft from E44 tissue, but only as high as 550 from the E49 donor. Up to 15,000 tyrosine hydroxylase-positive neurons were stained in the host monkey that received E44 tissue; only 1/10 as many were seen in each of the recipients of E49 day samples. The earlier donor grafts occupied as much as 15% of the caudate nucleus as seen in a single coronal section; summation of all sections that contained grafts at each placement from the E44 donor revealed average areas occupied by the grafts ranging from 3 to 8% of the caudate nucleus. In comparison, grafts produced from an E49 donor averaged between 2.4 and 5.4% of the area of the target. Qualitatively, grafts from each gestational stage showed well-developed dopamine neurons with morphological characteristics equivalent to those of all three ventral mesencephalic dopamine cell groups. The attainment of large, well-differentiated grafts with thousands of dopaminergic neurons from early gestation tissue suggests that optimal cell survival in primates is dependent on the degree of postgerminal development of the dopamine neuron. Neurite extension may be critical in this regard as well as other, at present, undefined factors. Maximal graft development and cell survival may be a critical element in the ability of neural grafts to reverse a neurological disability and to maintain improvement in the event of continued degeneration of host dopamine neurons.

Co-grafts of embryonic dopamine neurons and adult sciatic nerve into the denervated striatum enhance behavioral and morphological recovery in rats

We have recently demonstrated that a diffusible factor(s) derived from explanted adult rat sciatic nerve can increase the number and neurite outgrowth of embryonic rat dopamine (DA) neurons in culture. The present study extends this finding to compare DA neuron-sciatic nerve co-grafts to grafts of DA-rich neural tissue alone for behavioral and morphological effects in rats with unilateral nigrostriatal lesions of the DA pathway. Our results indicate that the presence of a co-grafted segment of sciatic nerve increased the likelihood of rapid behavioral recovery and promoted complete recovery mediated by small grafts that yielded only modest behavioral changes in the absence of co-grafted nerve. These behavioral effects were accompanied by a modest increase in survival of grafted tyrosine hydroxylase-positive neurons in the striatum and a more pronounced increase in the area and density of striatal reinnervation provided by grafted DA neurons in co-grafted animals. This evidence supports the view that a diffusible product of explanted peripheral nerve acts as a growth-promoting factor for embryonic DA neurons and that the presence of this factor augments the behavioral efficacy of grafted DA neurons.

Divergence of biological and chronological aging: evidence from rodent studies

Literature on aging populations of rodents supports the intuitive view that significant functional variation exists among like-aged, elderly individuals: chronological age as a solitary measure is a poor indicator of biological age. In this report, we review a variety of studies which classify aged rodents based on genetic and/or behavioral similarities, in addition to chronological age, and have provided valuable neurobiological and physiological information on age-related changes which accompany functional impairments, or the lack of them. Beyond their descriptive value for gerontological research, these findings suggest ways in which biological aging can be manipulated to promote good function in aged individuals.